REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
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Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
2003 Analog Devices, Inc. All rights reserved.
ADM1027
*
dBCOOL
TM
Remote Thermal
Controller and Voltage Monitor
*Protected by U.S. Patent Nos. 6,188,189; 6,169,442; 6,097,239; 5,982,221;
and 5,867,012. Other patents pending.
FEATURES
Monitors up to 5 Supply Voltages
Controls and Monitors up to 4 Fan Speeds
1 On-Chip and 2 Remote Temperature Sensors
Monitors up to 5 Processor VID Bits
Automatic Fan Speed Control Mode Controls System
Cooling Based on Measured Temperature
Enhanced Acoustic Mode Dramatically Reduces User
Perception of Changing Fan Speeds
2-Wire and 3-Wire Fan Speed Measurement
Limit Comparison of All Monitored Values
Meets SMBus 2.0 Electrical Specifications
(Fully SMBus 1.1 Compliant)
APPLICATIONS
Low Acoustic Noise PCs
Networking and Telecommunications Equipment
FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The ADM1027 dBCOOL controller is a complete systems
monitor and multiple PWM fan controller for noise sensitive
applications requiring active system cooling. It can monitor
12 V, 5 V, 2.5 V CPU supply voltage, plus its own supply volt-
age. It can monitor the temperature of up to two remote sensor
diodes, plus its own internal temperature. It can measure and
control the speed of up to four fans so that they operate at the
lowest possible speed for minimum acoustic noise. The auto-
matic fan speed control loop optimizes fan speed for a given
temperature. Once the control loop parameters are programmed,
the ADM1027 can vary fan speed without CPU intervention.
BAND GAP
REFERENCE
10-BIT
ADC
INPUT
SIGNAL
CONDITIONING
AND
ANALOG
MULTIPLEXER
GND
SERIAL BUS
INTERFACE
SCL SDA
VID
REGISTER
FAN SPEED
COUNTER
ADDRESS
POINTER
REGISTER
ADM1027
VALUE AND
LIMIT
REGISTERS
LIMIT
COMPARATORS
PWM
CONFIGURATION
REGISTERS
INTERRUPT
STATUS
REGISTERS
BAND GAP
TEMP. SENSOR
VID4
VID3
VID2
VID1
VID0
PWM
REGISTERS
AND
CONTROLLERS
PWM1
PWM2
V
CC
TO ADM1027
AUTOMATIC
FAN SPEED
CONTROL
PWM3
TACH1
TACH2
TACH3
TACH4
INTERRUPT
MASKING
SMBALERT
ACOUSTIC
ENHANCEMENT
CONTROL
V
CC
D1+
D1
D2+
D2
+5V
IN
+12V
IN
+2.5V
IN
V
CCP
SMBUS
ADDRESS
SELECTION
ADDR EN
ADDR
SELECT
REV. A
2
ADM1027SPECIFICATIONS
1, 2, 3, 4
(T
A
= T
MIN
to T
MAX
(0 C to 105 C), V
CC
= V
MIN
to V
MAX
(3 V to 5.5 V),
unless otherwise noted.)
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
POWER SUPPLY
Supply Voltage
3.0
3.3
5.5
V
Supply Current, I
CC
1.4
3
mA
Interface Inactive, ADC Active
TEMP-TO-DIGITAL CONVERTER
Local Sensor Accuracy
3
o
C
0
o
C T
A
105
o
C
2
o
C
0
o
C T
A
70
o
C
1
o
C
T
A
= 40
o
C
Resolution
0.25
o
C
Remote Diode Sensor Accuracy
3
o
C
0
o
C T
D
120
o
C
1.5
o
C
0
o
C T
D
120
o
C; 0
o
C T
A
70
o
C
1
o
C
T
A
= 40
o
C
o
C
0
o
C T
D
120
o
C; T
A
= 40
o
C
Resolution
0.25
o
C
Remote Sensor Source Current
200
mA
High Level
12
mA
Low Level
ANALOG-TO-DIGITAL CONVERTER
(INCLUDING MUX AND ATTENUATORS)
Total Unadjusted Error, TUE
0.5
1
%
All ADC Inputs except 12 V
1.5
%
12 V Input
Differential Nonlinearity, DNL
1
LSB
8 Bits
Power Supply Sensitivity
0.1
%/V
Conversion Time (Voltage Input)
11.38
12.29
ms
Averaging Enabled
Conversion Time (Local Temperature)
12.09
13.05
ms
Averaging Enabled
Conversion Time (Remote Temperature)
25.59
27.64
ms
Averaging Enabled
Total Monitoring Cycle Time
120.17
129.78
ms
Averaging Enabled
Total Monitoring Cycle Time
13.51
14.59
ms
Averaging Disabled
Input Resistance
80
140
250
k
FAN RPM-TO-DIGITAL CONVERTER
Accuracy
6
%
0
o
C T
A
70
o
C
8
%
3.0 V V
CC
3.6 V
Full-Scale Count
65,535
Nominal Input RPM
109
RPM
Fan Count = 0xBFFF
329
RPM
Fan Count = 0x3FFF
5,000
RPM
Fan Count = 0x0438
10,000
RPM
Fan Count = 0x021C
Internal Clock Frequency
82.8
90
97.2
kHz
OPEN-DRAIN DIGITAL OUTPUTS,
PWM1PWM3, XTO
Current Sink, I
OL
8.0
mA
Output Low Voltage, V
OL
0.4
V
I
OUT
= 8.0 mA, V
CC
= 3.3 V
High Level Output Current, I
OH
0.1
1
mA
V
OUT
= V
CC
REV. A
ADM1027
3
Parameter
Min
Typ
Max
Unit
Test Conditions/Comment
OPEN-DRAIN SERIAL DATA BUS
OUTPUT (SDA)
Output Low Voltage, V
OL
0.4
V
I
OUT
= 4.0 mA, V
CC
= 3.3 V
High Level Output Current, I
OH
0.1
1
mA
V
OUT
= V
CC
SMBUS DIGITAL INPUTS
(SCL, SDA)
Input High Voltage, V
IH
2.0
V
Input Low Voltage, V
IL
0.4
V
Hysteresis
500
mV
DIGITAL INPUT LOGIC LEVELS
(VID04)
Input High Voltage, V
IH
1.7
V
Input Low Voltage, V
IL
0.8
V
DIGITAL INPUT LOGIC LEVELS
(TACH INPUTS)
Input High Voltage, V
IH
2.0
V
5.5
V
Maximum Input Voltage
Input Low Voltage, V
IL
0.8
V
0.3
V
Minimum Input Voltage
Hysteresis
0.5
V p-p
DIGITAL INPUT CURRENT
Input High Current, I
IH
1
mA
V
IN
= V
CC
Input Low Current, I
IL
1
mA
V
IN
= 0
Input Capacitance, C
IN
5
pF
SERIAL BUS TIMING
Clock Frequency, f
SCLK
10
100
kHz
See Figure 1
Glitch Immunity, t
SW
50
ns
See Figure 1
Bus Free Time, t
BUF
4.7
ms
See Figure 1
Start Setup Time, t
SU;STA
4.7
ms
See Figure 1
Start Hold Time, t
HD;STA
4.0
ms
See Figure 1
SCL Low Time, t
LOW
4.7
ms
See Figure 1
SCL High Time, t
HIGH
4.0
50
ms
See Figure 1
SCL, SDA Rise Time, t
r
1000
ns
See Figure 1
SCL, SDA Fall Time, t
f
300
ms
See Figure 1
Data Setup Time, t
SU;DAT
250
ns
See Figure 1
Data Hold Time, t
HD;DAT
300
ns
See Figure 1
Detect Clock Low Timeout, t
TIMEOUT
15
35
ms
Can Be Optionally Disabled
NOTES
1
All voltages are measured with respect to GND, unless otherwise specified.
2
Typicals are at T
A
= 40
C and represent the most likely parametric norm.
3
Logic inputs will accept input high voltages up to V
MAX
even when the device is operating down to V
MIN
.
4
Timing specifications are tested at logic levels of V
IL
= 0.8 V for a falling edge and V
IH
= 2.0 V for a rising edge.
Specifications subject to change without notice.
REV. A
4
ADM1027
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although the
ADM1027 features proprietary ESD protection circuitry, permanent damage may occur on devices
subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended
to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
ABSOLUTE MAXIMUM RATINGS
*
Positive Supply Voltage (V
CC
) . . . . . . . . . . . . . . . . . . . . . 6.5 V
Voltage on 12 V
IN
Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 V
Voltage on Any Other Input or Output Pin . . . . 0.3 V to +6.5 V
Input Current at Any Pin . . . . . . . . . . . . . . . . . . . . . . . .
5 mA
Package Input Current . . . . . . . . . . . . . . . . . . . . . . . .
20 mA
Maximum Junction Temperature (T
J MAX
) . . . . . . . . . . 150
C
Storage Temperature Range . . . . . . . . . . . . . 65
C to +150C
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215
C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
C
ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000 V
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
PIN CONFIGURATION
TOP VIEW
(Not to Scale)
24
23
22
21
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
9
10
11
12
ADM1027
TACH2
TACH1
PWM2/
SMBALERT
TACH3
VID3
SDA
SCL
GND
V
CC
VID2
VID1
VID0
PWM3/
ADDRESS ENABLE
TACH4/ADDRESS SELECT
D2
D2+
D1
PWM1/XTO
V
CCP
2.5V
IN
12V
IN
D1+
VID4
5V
IN
ORDERING GUIDE
Model
Temperature Range
Package Description
Package Option
ADM1027
0C to 105C
24-Lead QSOP
RQ-24
THERMAL CHARACTERISTICS
24-Lead QSOP Package:
q
JA
= 123
C/W, q
JC
= 27
C/W
P
S
t
SU; DAT
t
HIGH
t
F
t
HD; DAT
t
R
t
LOW
t
SU; STO
P
S
SCL
SDA
t
HD; STA
t
HD; STA
t
SU; STA
t
BUF
Figure 1. Diagram for Serial Bus Timing
REV. A
ADM1027
5
PIN FUNCTION DESCRIPTIONS
Pin
Mnemonic
Description
1
SDA
Digital I/O (Open-Drain). SMBus bidirectional serial data. Requires SMBus pull-up.
2
SCL
Digital Input (Open-Drain). SMBus serial clock input. Requires SMBus pull-up.
3
GND
Ground Pin for the ADM1027.
4
V
CC
Power Supply. Can be powered by 3.3 V standby if monitoring in low power states is required.
V
CC
is also monitored through this pin. The ADM1027 can also be powered from a 5 V supply.
Setting Bit 7 of Configuration Register 1 (Reg. 0x40) rescales the V
CC
input attenuators to
correctly measure a 5 V supply.
5
VID0
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
6
VID1
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
7
VID2
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
8
VID3
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
9
TACH3
Digital Input (Open-Drain). Fan tachometer input to measure speed of Fan 3. Can be
reconfigured as an analog input (AIN3) to measure the speed of 2-wire fans.
10
PWM2/
SMBALERT
Digital Output (Open-Drain). Requires 10 k
W typical pull-up. Pulsewidth modulated output
to control Fan 2 speed. This pin may be reconfigured as an
SMBALERT interrupt output to
signal out-of-limit conditions.
11
TACH1
Digital Input (Open-Drain). Fan tachometer input to measure speed of Fan 1. Can be
reconfigured as an analog input (AIN1) to measure the speed of 2-wire fans.
12
TACH2
Digital Input (Open-Drain). Fan tachometer input to measure speed of Fan 2. Can be
reconfigured as an analog input (AIN2) to measure the speed of 2-wire fans.
13
PWM3/
ADDRESS ENABLE
Digital I/O (Open-Drain). Pulsewidth modulated output to control Fan 3 speed. Requires
10 k
W typical pull-up. If pulled low on power-up, this places the ADM1027 into address
select mode, and the state of Pin 14 will determine the ADM1027's slave address.
14
TACH4/ADDRESS SELECT
Digital Input (Open-Drain). Fan tachometer input to measure speed of Fan 4. Can be reconfigured
as an analog input (AIN4) to measure the speed of 2-wire fans. If in address select mode,
this pin determines the SMBus device address.
15
D2
Cathode Connection to Second Thermal Diode.
16
D2+
Anode Connection to Second Thermal Diode.
17
D1
Cathode Connection to First Thermal Diode.
18
D1+
Anode Connection to First Thermal Diode.
19
VID4
Digital Input (Open-Drain). Voltage supply readouts from CPU. This value is read into the
VID register (Reg. 0x43).
20
5V
IN
Analog Input. Monitors 5 V power supply.
21
12V
IN
Analog Input. Monitors 12 V power supply.
22
2.5V
IN
Analog Input. Monitors 2.5 V supply, typically a chipset voltage.
23
V
CCP
Analog Input. Monitors processor core voltage (0 V to 3 V).
24
PWM1/XTO
Digital Output (Open-Drain). Pulsewidth modulated output to control Fan 1 speed. Requires
10 k
W typical pull-up. Also functions as the output from the XOR tree in XOR test mode.
REV. A
6
ADM1027
FUNCTIONAL DESCRIPTION
General Description
The ADM1027 is a complete systems monitor and multiple fan
controller for any system requiring monitoring and cooling. The
device communicates with the system via a serial system
management bus. The serial bus controller has an optional
address line for device selection (Pin 14), a serial data line
for reading and writing addresses and data (Pin 1), and an input
line for the serial clock (Pin 2). All control and programming
functions of the ADM1027 are performed over the serial bus. In
addition, one of the pins can be reconfigured as an
SMBALERT
output to indicate out-of-limit conditions.
Measurement Inputs
The device has six measurement inputs, four for voltage and
two for temperature. It can also measure its own supply voltage
and can measure ambient temperature with its on-chip tempera-
ture sensor.
Pins 20 to 23 are analog inputs with on-chip attenuators,
configured to monitor 5 V, 12 V, 2.5 V, and the processor core
voltage (2.25 V input), respectively.
Power is supplied to the chip via Pin 4, which the system also
uses to monitor V
CC
. In PCs, this pin is normally connected to a
3.3 V standby supply. This pin can, however, be connected to a
5 V supply and monitor it without overranging.
Remote temperature sensing is provided by the D1+/ and
D2+/ inputs, to which diode-connected, external temperature-
sensing transistors such as a 2N3906 or CPU thermal diode
may be connected.
The ADC also accepts input from an on-chip band gap tem-
perature sensor that monitors system ambient temperature.
Sequential Measurement
When the ADM1027 monitoring sequence is started, it cycles
sequentially through the measurement of analog inputs and the
temperature sensors. Measured values from these inputs are
stored in value registers. These can be read out over the serial
bus, or can be compared with programmed limits stored in the
limit registers. The results of out-of-limit comparisons are stored
in the status registers, which can be read over the serial bus to
flag out-of-limit conditions.
Processor Voltage ID
Five digital inputs (VID0 to VID4 -- Pins 5 to 8 and 19) read
the processor Voltage ID code and store it in the VID register,
from which it can be read out by the management system over
the serial bus. The VID code monitoring function is compatible
with both VRM9.x and future VRM10 solutions. The VID code
monitoring function is compatible with VRM9.x.
ADM1027 Address Selection
Pin 13 is the dual function PWM3/
ADDRESS ENABLE pin.
If Pin 13 is pulled low on power-up, the ADM1027 will read the
state of Pin 14 (TACH4/ADDRESS SELECT pin) to determine
the ADM1027 slave address. If Pin 13 is high on power-up, then
the ADM1027 will default to SMBus slave address 0x5C. This
function is described later in more detail.
Internal Registers of the ADM1027
A brief description of the ADM1027's principal internal regis-
ters follows. More detailed information on the function of each
register is given in Tables IV to XXXVI.
Configuration Registers
Provide control and configuration of the ADM1027, including
alternate pinout functionality.
Address Pointer Register
Contains the address that selects one of the other internal registers.
When writing to the ADM1027, the first byte of data is always a
register address, which is written to the Address Pointer Register.
Status Registers
Provide the status of each limit comparison and are used to
signal out-of-limit conditions on the temperature, voltage, or
fan speed channels. If Pin 10 is configured as
SMBALERT,
then this pin will assert low whenever a status bit gets set.
Interrupt Mask Registers
Allow each interrupt status event to be masked when Pin 10 is
configured as an
SMBALERT output. This affects only the
SMBALERT output and not the bits in the status register.
VID Register
The status of the VID0 to VID4 pins of the processor can be
read from this register.
Value and Limit Registers
The results of analog voltage inputs, temperature, and fan speed
measurements are stored in these registers, along with their limit
values.
Offset Registers
Allow each temperature channel reading to be offset by a twos
complement value written to these registers.
T
MIN
Registers
Program the starting temperature for each fan under automatic
fan speed control.
T
RANGE
Registers
Program the temperature-to-fan speed control slope in automatic
Fan Speed Control Mode for each PWM output.
Enhance Acoustics Registers
Allow each PWM output controlling fan to be tweaked to enhance
the system's acoustics.
REV. A
Typical Performance CharacteristicsADM1027
7
LEAKAGE RESISTANCE (M )
REMO
TE
TEMPERA
TURE ERR
OR (
C)
15
10
20
1.0
3.3
100.0
10.0
30.0
0
5
10
15
5
DXP TO GND
DXP TO V
CC
(3.3V)
TPC 1. Remote Temperature
Error vs. Leakage Resistance
FREQUENCY (Hz)
REMO
TE
TEMPERA
TURE ERR
OR (
C)
14.0
12.0
2.0
100k
550k
50M
5M
6.0
4.0
0
2.0
10.0
8.0
100mV
250mV
TPC 4. Remote Temperature Error
vs. Power Supply Noise Frequency
FREQUENCY (Hz)
REMO
TE
TEMPERA
TURE ERR
OR (
C)
16.0
60k
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0
2.0
110k
1M
10M
50M
10mV
20mV
TPC 7. Remote Temperature Error
vs. Differential Mode Noise
Frequency
DXP DXN CAPACITANCE (nF)
REMO
TE
TEMPERA
TURE ERR
OR (
C)
3
1
0
3
6
9
12
15
18
21
24
27
2.2
3.3
4.7
10.0
22.0
47.0
30
33
36
REMOTE TEMPERATURE
ERROR ( C)
TPC 2. Remote Temperature Error
vs. Capacitance between D+ and D
FREQUENCY (Hz)
LOCAL
TEMPERA
TURE ERR
OR (
C)
12.5
10.0
5.0
100k
550k
50M
5M
5.0
2.5
2.5
0
7.5
100mV
250mV
TPC 5. Local Temperature Error vs.
Power Supply Noise Frequency
FREQUENCY (Hz)
REMO
TE
TEMPERA
TURE ERR
OR (
C)
40.0
10k
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0
5.0
10.0
100k
1M
10M
20mV
40mV
100mV
TPC 8. Remote Temperature Error
vs. Common Mode Noise Frequency
TEMPERATURE ( C)
REMO
TE
TEMPERA
TURE ERR
OR (
C)
3
40
2
1
0
1
2
3
0
40
80
120
3 SIGMA
+3 SIGMA
TPC 3. Remote Temperature Error
vs. Actual Temperature
1.90
1.85
1.80
1.75
1.70
1.65
1.60
1.55
1.50
1.45
1.40
2.50
2.60 3.00 3.40 3.80 4.20
4.60 5.00 5.40
5.50
SUPPL
Y CURRENT (mA)
TPC 6. Supply Current vs.
Supply Voltage
REV. A
8
ADM1027
SERIAL BUS INTERFACE
Control of the ADM1027 is carried out using the serial System
Management Bus (SMBus). The ADM1027 is connected to this
bus as a slave device, under the control of a master controller.
The ADM1027 has a 7-bit serial bus address. When the device
is powered up with Pin 13 (PWM3/
ADDRESS ENABLE) high,
the ADM1027 will have a default SMBus address of 0101110
or 0x5C. If more than one ADM1027 is to be used in a system,
then each ADM1027 should be placed in address select mode
by strapping Pin 13 low on power-up. The logic state of Pin 14
then determines the device's SMBus address.
Table I. ADM1027 Address Select Mode
Pin 13 State
Pin 14 State
Address
0
Low (10 k
W to GND) 0101100 (0x58)
0
High (10 k
W pull-up) 0101101 (0x5A)
1
Don't Care
0101110 (0x5C)
(default)
ADM1027
14
13
ADDR_SEL
PWM3/
ADDR_EN
V
CC
10k
ADDRESS = 0x5C
Figure 2. Default SMBus Address = 0x5C
ADM1027
14
13
ADDR_SEL
PWM3/
ADDR_EN
10k
ADDRESS = 0x58
Figure 3. SMBus Address = 0x58 (Pin 14 = 0)
The device address is sampled and latched on the first valid
SMBus transaction, so any attempted addressing changes made
thereafter will have no immediate effect.
The facility to make hardwired changes to the SMBus slave
address allows the user to avoid conflicts with other devices
sharing the same serial bus (for example, if more than one
ADM1027 is used in a system).
Once the SMBus address has been assigned, these pins return
to their original function. However, since the circuits required
to set up the SMBus address are unworkable with the PWM
and TACH circuits, it would require the use of muxes to switch
in and out the correct circuit at the correct time.
ADM1027
ADDR_SEL
PWM3/
ADDR_EN
ADDRESS = 0x5A
14
13
V
CC
10k
Figure 4. SMBus Address = 0x5A (Pin 14 = 1)
ADM1027
14
13
ADDR_SEL
PWM3/
ADDR_EN
V
CC
10k
DO NOT LEAVE ADDR_EN
UNCONNECTED! CAN
CAUSE UNPREDICTABLE
ADDRESSES
NC
Figure 5. Unpredictable SMBus Address if Pin 13
is Unconnected
Care should be taken to ensure that Pin 13 (PWM3/
ADDR_EN) is either tied high or low. Leaving Pin 13
floating could cause the ADM1027 to power up with an
unexpected address.
Note that if the ADM1027 is placed into address select mode,
Pins 13 and 14 can be used as their alternate functions once
address assignment has taken place (PWM3, TACH4). Care
should be taken using muxes to connect in the appropriate circuit
at the appropriate time.
The serial bus protocol operates as follows:
1. The master initiates data transfer by establishing a start
condition, defined as a high to low transition on the serial
data line SDA while the serial clock line SCL remains high.
This indicates that an address/data stream will follow. All
slave peripherals connected to the serial bus respond to the
start condition and shift in the next eight bits, consisting
of a 7-bit address (MSB first) plus the R/
W bit, which deter-
mines the direction of the data transfer, i.e., whether data
will be written to or read from the slave device.
The peripheral whose address corresponds to the transmitted
address responds by pulling the data line low during the low
period before the ninth clock pulse, known as the acknowledge
bit. All other devices on the bus now remain idle while the
selected device waits for data to be read from or written to
it. If the R/
W bit is a 0, the master will write to the slave
device. If the R/
W bit is a 1, the master will read from the
slave device.
2. Data is sent over the serial bus in sequences of nine clock
pulses, eight bits of data followed by an acknowledge bit
from the slave device. Transitions on the data line must
occur during the low period of the clock signal and remain
stable during the high period, as a low to high transition
when the clock is high may be interpreted as a stop signal.
The number of data bytes that can be transmitted over the
serial bus in a single read or write operation is limited
only by what the master and slave devices can handle.
3. When all data bytes have been read or written, stop conditions
are established. In write mode, the master will pull the
data line high during the 10th clock pulse to assert a
stop condition. In read mode, the master device will
override the acknowledge bit by pulling the data line high
during the low period before the ninth clock pulse. This is
known as No Acknowledge. The master will then take the
data line low during the low period before the 10th clock
pulse, then high during the 10th clock pulse to assert a
stop condition.
REV. A
ADM1027
9
Any number of bytes of data can be transferred over the serial
bus in one operation. However, it is not possible to mix read
and write in one operation because the type of operation is
determined at the beginning and subsequently cannot be changed
without starting a new operation.
In the case of the ADM1027, write operations contain either
one or two bytes, and read operations contain one byte and
perform the following functions:
To write data to one of the device data registers or read data
from it, the address pointer register must be set so the correct
data register is addressed, then data can be written into that
register or read from it. The first byte of a write operation always
contains an address that is stored in the address pointer register.
If data is to be written to the device, then the write operation
contains a second data byte that is written to the register selected
by the address pointer register.
This is illustrated in Figure 6. The device address is sent over
the bus followed by R/W being set to 0. This is followed by two
data bytes. The first data byte is the address of the internal data
register to be written to, which is stored in the address pointer
register. The second data byte is the data to be written to the
internal data register.
When reading data from a register, there are two possibilities:
1. If the ADM1027 address pointer register value is unknown or
not the desired value, it is first necessary to set it to the correct
value before data can be read from the desired data register.
This is done by performing a write to the ADM1027 as before,
but only sending the data byte containing the register address,
as data is not to be written to the register. This is shown in
Figure 7.
A read operation is then performed consisting of the serial
bus address, R/W bit set to 1, followed by the data byte read
from the data register. This is shown in Figure 8.
2. If the address pointer register is known to be already at the
desired address, data can be read from the corresponding data
register without first writing to the address pointer register,
so Figure 7 can be omitted.
R/W
0
SCL
SDA
1
0
1
1
A1
A0
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1027
START BY
MASTER
FRAME 1
SERIAL BUS ADDRESS
BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
1
9
1
ACK. BY
ADM1027
9
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1027
STOP BY
MASTER
FRAME 3
DATA
BYTE
1
9
SCL (CONTINUED)
SDA (CONTINUED)
Figure 6. Writing a Register Address to the Address Pointer Register, Then Writing Data to the Selected Register
R/W
0
SCL
SDA
1
0
1
1
A1
A0
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1027
STOP BY
MASTER
START BY
MASTER
FRAME 1
SERIAL BUS ADDRESS
BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
1
9
1
ACK. BY
ADM1027
9
Figure 7. Writing to the Address Pointer Register Only
R/W
0
SCL
SDA
1
0
1
1
A1
A0
D7
D6
D5
D4
D3
D2
D1
D0
NO ACK. BY
MASTER
STOP BY
MASTER
START BY
MASTER
FRAME 1
SERIAL BUS ADDRESS
BYTE
FRAME 2
DATA BYTE FROM ADM1027
1
9
1
ACK. BY
ADM1027
9
Figure 8. Reading Data from a Previously Selected Register
REV. A
10
ADM1027
Notes
1. It is possible to read a data byte from a data register without
first writing to the address pointer register if the address
pointer register is already at the correct value. However, it is
not possible to write data to a register without writing to the
address pointer register, because the first data byte of a write
is always written to the address pointer register.
2. In Figures 6 to 8, the serial bus address is shown as the default
value 01011(A1)(A0), where A1 and A0 are set by the address
select mode function previously defined.
3. In addition to supporting the send byte and receive byte
protocols, the ADM1027 also supports the read byte protocol
(see System Management Bus specifications Rev. 2.0 for
more information).
4. If it is required to perform several read or write operations in
succession, the master can send a repeat start condition instead
of a stop condition to begin a new operation.
ADM1027 WRITE OPERATIONS
The SMBus specification defines several protocols for different
types of read and write operations. The ones used in the
ADM1027 are discussed below. The following abbreviations are
used in the diagrams:
S START
P STOP
R READ
W WRITE
A ACKNOWLEDGE
A NO ACKNOWLEDGE
The ADM1027 uses the following SMBus write protocols:
Send Byte
In this operation, the master device sends a single command
byte to a slave device, as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address followed by the
write bit (low).
3. The addressed slave device asserts ACK on SDA.
4. The master sends a command code.
5. The slave asserts ACK on SDA.
6. The master asserts a stop condition on SDA and the
transaction ends.
For the ADM1027, the send byte protocol is used to write a
register address to RAM for a subsequent single byte read from
the same address. This is illustrated in Figure 9.
S
SLAVE
ADDRESS
W A
A P
1
2
3
4
5
6
REGISTER
ADDRESS
Figure 9. Setting a Register Address for Subsequent Read
If it is required to read data from the register immediately after
setting up the address, the master can assert a repeat start con-
dition immediately after the final ACK and carry out a single
byte read without asserting an intermediate stop condition.
Write Byte
In this operation, the master device sends a command byte and
one data byte to the slave device, as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address followed by the
write bit (low).
3. The addressed slave device asserts ACK on SDA.
4. The master sends a command code.
5. The slave asserts ACK on SDA.
6. The master sends a data byte.
7. The slave asserts ACK on SDA.
8. The master asserts a stop condition on SDA to end the
transaction.
This is illustrated in Figure 10.
S
SLAVE
ADDRESS
W A
1
2
3
4
5
6
A DATA A P
7 8
REGISTER
ADDRESS
Figure 10. Single Byte Write to a Register
ADM1027 READ OPERATIONS
The ADM1027 uses the following SMBus read protocols:
Receive Byte
This is useful when repeatedly reading a single register. The
register address needs to have been set up previously. In this
operation, the master device receives a single byte from a slave
device, as follows:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address followed by the
read bit (high).
3. The addressed slave device asserts ACK on SDA.
4. The master receives a data byte.
5. The master asserts NO ACK on SDA.
6. The master asserts a stop condition on SDA and the trans-
action ends.
In the ADM1027, the receive byte protocol is used to read a
single byte of data from a register whose address has previously
been set by a send byte or write byte operation.
S
SLAVE
ADDRESS
R
A DATA
A P
1
2
3
4
5
6
Figure 11. Single Byte Read from a Register
Alert Response Address
Alert Response Address (ARA) is a feature of SMBus devices,
which allows an interrupting device to identify itself to the host
when multiple devices exist on the same bus.
The SMBALERT output can be used as an interrupt output or
can be used as an SMBALERT. One or more outputs can be
connected to a common SMBALERT line connected to the
master. If a device's SMBALERT line goes low, the following
procedure occurs:
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the alert response
address (ARA = 0001 100). This is a general call address that
must not be used as a specific device address.
3. The device whose SMBALERT output is low responds to
the alert response address, and the master reads its device
address. The address of the device is now known and it can
be interrogated in the usual way.
4. If more than one device's SMBALERT output is low, the one
with the lowest device address will have priority, in accordance
with normal SMBus arbitration.
REV. A
ADM1027
11
5. Once the ADM1027 has responded to the alert response
address, the master must read the status registers and the
SMBALERT will only be cleared if the error condition has
gone away.
SMBus Timeout
The ADM1027 includes an SMBus timeout feature. If there is
no SMBus activity for a minimum of 15 ms and a maximum of
35 ms, the ADM1027 assumes that the bus is locked and releases
the bus. This prevents the device from locking or holding the
SMBus expecting data. Some SMBus controllers cannot handle
the SMBus timeout feature, so it can be disabled.
CONFIGURATION REGISTER 1 Register 0x40
<6>
TODIS = 0; SMBus timeout enabled (default)
<6>
TODIS = 1; SMBus timeout disabled
VOLTAGE MEASUREMENT INPUTS
The ADM1027 has four external voltage measurement channels.
It can also measure its own supply voltage, V
CC
.
Pins 20 to 23 are dedicated to measuring 5 V, 12 V, 2.5 V supplies
and the processor core voltage V
CCP
(0 V to 3 V input). The
V
CC
supply voltage measurement is carried out through the V
CC
pin (Pin 4). Setting Bit 7 of Configuration Register 1 (Reg. 0x40)
allows a 5 V supply to power the ADM1027 and be measured
without overranging the V
CC
measurement channel. The 2.5 V
input can be used to monitor a chipset supply voltage in com-
puter systems.
ANALOG-TO-DIGITAL CONVERTER
All analog inputs are multiplexed into the on-chip, successive
approximation, analog-to-digital converter. This has a resolu-
tion of 10 bits. The basic input range is 0 V to 2.25 V, but the
inputs have built-in attenuators to allow measurement of 2.5 V,
3.3 V, 5 V, 12 V and the processor core voltage V
CCP
, without
any external components. To allow for the tolerance of these
supply voltages, the ADC produces an output of 3/4 full scale
(768 decimal or 300 hex) for the nominal input voltage, and so
has adequate headroom to cope with overvoltages.
INPUT CIRCUITRY
The internal structure for the analog inputs is shown in Figure 12.
Each input circuit consists of an input protection diode, an
attenuator, and a capacitor to form a first order low-pass filter
that gives the input immunity to high frequency noise.
VOLTAGE MEASUREMENT REGISTERS
Reg. 0x20 2.5 V Reading = 0x00 default
Reg. 0x21 V
CCP
Reading
= 0x00 default
Reg. 0x22 V
CC
Reading
= 0x00 default
Reg. 0x23 5 V Reading = 0x00 default
Reg. 0x24 12 V Reading = 0x00 default
VOLTAGE MEASUREMENT LIMIT REGISTERS
Associated with each voltage measurement channel are high and
low limit registers. Exceeding the programmed high or low limit
causes the appropriate status bit to be set. Exceeding either limit
can also generate SMBALERT interrupts.
Reg. 0x44 2.5 V Low Limit = 0x00 default
Reg. 0x45 2.5 V High Limit = 0xFF default
Reg. 0x46 V
CCP
Low Limit
= 0x00 default
Reg. 0x47 V
CCP
High Limit
= 0xFF default
Reg. 0x48 V
CC
Low Limit
= 0x00 default
Reg. 0x49 V
CC
High Limit
= 0xFF default
Reg. 0x4A 5 V Low Limit = 0x00 default
Reg. 0x4B 5 V High Limit = 0xFF default
Reg. 0x4C 12 V Low Limit = 0x00 default
Reg. 0x4D 12 V High Limit = 0xFF default
30pF
120k
30pF
93k
MUX
30pF
68k
30pF
45k
105k
35pF
35k
94k
71k
47k
20k
12V
IN
5V
IN
3.3V
IN
2.5V
IN
V
CCPIN
Figure 12. Structure of Analog Inputs
Table II shows the input ranges of the analog inputs and output
codes of the 10-bit A/D converter.
When the ADC is running, it samples and converts a voltage
input in 711
ms, and averages 16 conversions to reduce noise.
Therefore a measurement on any input takes nominally 11.38 ms.
REV. A
12
ADM1027
Table II. 10-Bit A/D Output Code vs. V
IN
Input Voltage
A/D Output
12 V
IN
5 V
IN
V
CC
(3.3 V
IN
)
*
2.5 V
IN
V
CCPIN
Decimal
Binary (10 Bits)
<0.0156
<0.0065
<0.0042
<0.0032
<0.00293
0
00000000 00
0.0156 0.0312
0.0065 0.0130
0.0042 0.0085
0.0032 0.0065
0.0293 0.0058
1
00000000 01
0.0312 0.0469
0.0130 0.0195
0.0085 0.0128
0.0065 0.0097
0.0058 0.0087
2
00000000 10
0.0469 0.0625
0.0195 0.0260
0.0128 0.0171
0.0097 0.0130
0.0087 0.0117
3
00000000 11
0.0625 0.0781
0.0260 0.0325
0.0171 0.0214
0.0130 0.0162
0.0117 0.0146
4
00000001 00
0.0781 0.0937
0.0325 0.0390
0.0214 0.0257
0.0162 0.0195
0.0146 0.0175
5
00000001 01
0.0937 0.1093
0.0390 0.0455
0.0257 0.0300
0.0195 0.0227
0.0175 0.0205
6
00000001 10
0.1093 0.1250
0.0455 0.0521
0.0300 0.0343
0.0227 0.0260
0.0205 0.0234
7
00000001 11
0.1250 0.1406
0.0521 0.0586
0.0343 0.0386
0.0260 0.0292
0.0234 0.0263
8
00000010 00
4.0000 4.0156
1.6675 1.6740
1.1000 1.1042
0.8325 0.8357
0.7500 0.7529
256 (1/4 scale)
01000000 00
8.0000 8.0156
3.3300 3.3415
2.2000 2.2042
1.6650 1.6682
1.5000 1.5029
512 (1/2 scale)
10000000 00
12.0000 12.0156
5.0025 5.0090
3.3000 3.3042
2.4975 2.5007
2.2500 2.2529
768 (3/4 scale)
11000000 00
15.8281 15.8437
6.5983 6.6048
4.3527 4.3570
3.2942 3.2974
2.9677 2.9707
1013
11111101 01
15.8437 15.8593
6.6048 6.6113
4.3570 4.3613
3.2974 3.3007
2.9707 2.9736
1014
11111101 10
15.8593 15.8750
6.6113 6.6178
4.3613 4.3656
3.3007 3.3039
2.9736 2.9765
1015
11111101 11
15.8750 15.8906
6.6178 6.6244
4.3656 4.3699
3.3039 3.3072
2.9765 2.9794
1016
11111110 00
15.8906 15.9062
6.6244 6.6309
4.3699 4.3742
3.3072 3.3104
2.9794 2.9824
1017
11111110 01
15.9062 15.9218
6.6309 6.6374
4.3742 4.3785
3.3104 3.3137
2.9824 2.9853
1018
11111110 10
15.9218 15.9375
6.6374 6.4390
4.3785 4.3828
3.3137 3.3169
2.9853 2.9882
1019
11111110 11
15.9375 15.9531
6.6439 6.6504
4.3828 4.3871
3.3169 3.3202
2.9882 2.9912
1020
11111111 00
15.9531 15.9687
6.6504 6.6569
4.3871 4.3914
3.3202 3.3234
2.9912 2.9941
1021
11111111 01
15.9687 15.9843
6.6569 6.6634
4.3914 4.3957
3.3234 3.3267
2.9941 2.9970
1022
11111111 10
>15.9843
>6.6634
>4.3957
>3.3267
>2.9970
1023
11111111 11
*The V
CC
output codes listed assume that V
CC
is 3.3 V. If V
CC
input is reconfigured for 5 V operation (by setting Bit 7 of Configuration Register 1), then the V
CC
output codes are the same as for the 5 V
IN
column.
REV. A
ADM1027
13
VID CODE MONITORING
The ADM1027 has five dedicated voltage ID (VID code) inputs.
These are digital inputs that can be read back through the
VID register (Reg. 0x43) to determine the processor voltage
required/being used in the system. Five VID code inputs
support VRM9.x solutions.
VID CODE REGISTER Register 0x43
<0> = VID0
(reflects logic state of Pin 5)
<1> = VID1
(reflects logic state of Pin 6)
<2> = VID2
(reflects logic state of Pin 7)
<3> = VID3
(reflects logic state of Pin 8)
<4> = VID4
(reflects logic state of Pin 19)
ADDITIONAL ADC FUNCTIONS
A number of other functions are available on the ADM1027 to
offer the systems designer increased flexibility:
Turn Off Averaging
For each voltage measurement read from a value register,
16 readings have actually been made internally and the results
averaged before being placed into the value register. There may
be an instance where the user would like to speed up conversions.
Setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns
averaging off. This effectively gives a reading 16
faster than
711
ms, but the reading may be noisier.
Bypass Voltage Input Attenuators
Setting Bit 5 of Configuration Register 2 (Reg. 0x73) removes
the attenuation circuitry from the 2.5 V, V
CCP
, V
CC
, 5 V, and
12 V inputs. This allows the user to directly connect external
sensors or rescale the analog voltage measurement inputs for
other applications. The input range of the ADC without the
attenuators is 0 V to 2.25 V.
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the
ADM1027 into single-channel ADC conversion mode. In this
mode, the ADM1027 can be made to read a single voltage channel
only. If the internal ADM1027 clock is used, the selected input
will be read every 711
ms. The appropriate ADC channel is
selected by writing to Bits <7:5> of TACH1 minimum high
byte register (0x55).
Bits <7:5> Reg. 0x55
Channel Selected
000
2.5 V
001
V
CCP
010
V
CC
011
5 V
100
12 V
Configuration Register 2 (Reg. 0x73)
<4> = 1
Averaging off
<5> = 1
Bypass input attenuators
<6> = 1
Single-channel convert mode
TACH1 Minimum High Byte (Reg. 0x55)
<7:5>
Selects ADC channel for single-channel convert mode
REV. A
14
ADM1027
TEMPERATURE MEASUREMENT SYSTEM
Local Temperature Measurement
The ADM1027 contains an on-chip band gap temperature
sensor whose output is digitized by the on-chip 10-bit ADC.
The 8-bit MSB temperature data is stored in the local temp
register (Address 0x26). As both positive and negative tempera-
tures can be measured, the temperature data is stored in twos
complement format, as shown in Table III. Theoretically, the
temperature sensor and ADC can measure temperatures from
128
o
C to +127
o
C with a resolution of 0.25
o
C. However, this
exceeds the operating temperature range of the device (0
o
C to
105
o
C), so local temperature measurements outside this range
are not possible. Temperature measurement from 127
o
C to
+127
o
C is possible using a remote sensor.
Remote Temperature Measurement
The ADM1027 can measure the temperature of two remote
diode sensors or diode-connected transistors connected to
Pins 15 and 16, or 17 and 18.
The forward voltage of a diode or diode-connected transistor,
operated at a constant current, exhibits a negative temperature
coefficient of about 2 mV/
o
C. Unfortunately, the absolute
value of V
be
varies from device to device, and individual calibra-
tion is required to null this out, so the technique is unsuitable
for mass production. The technique used in the ADM1027 is to
measure the change in V
be
when the device is operated at two
different currents. This is given by
where:
K is Boltzmann's constant.
q is charge on the carrier.
T is absolute temperature in kelvins.
N is the ratio of the two currents.
Figure 13 shows the input signal conditioning used to measure
the output of a remote temperature sensor. This figure shows the
external sensor as a substrate transistor, provided for temperature
monitoring on some microprocessors. It could equally well be a
discrete transistor such as a 2N3904/06.
D+
D
REMOTE
SENSING
TRANSISTOR
I
N I
I
BIAS
V
DD
V
OUT+
TO ADC
V
OUT
BIAS
DIODE
LOW-PASS
FILTER
f
C
= 65kHz
THERMDA
THERMDC
CPU
Figure 13. Signal Conditioning for Remote Diode Temperature Sensors
DV
KT q
N
be
=
( )
ln
REV. A
ADM1027
15
If a discrete transistor is used, the collector will not be grounded,
and should be linked to the base. If a PNP transistor is used, the
base is connected to the D input and the emitter to the D+
input. If an NPN transistor is used, the emitter is connected to
the D input and the base to the D+ input. Figure 14 shows
how to connect the ADM1027 to an NPN or PNP transistor for
temperature measurement. To prevent ground noise from inter-
fering with the measurement, the more negative terminal of the
sensor is not referenced to ground, but is biased above ground
by an internal diode at the D input.
To measure
DV
be
, the sensor is switched between operating cur-
rents of I and N I. The resulting waveform is passed through a
65 kHz low-pass filter to remove noise, and to a chopper-stabilized
amplifier that performs the functions of amplification and recti-
fication of the waveform to produce a dc voltage proportional to
DV
be
. This voltage is measured by the ADC to give a temperature
output in 10-bit, twos complement format. To further reduce
the effects of noise, digital filtering is performed by averaging the
results of 16 measurement cycles. A remote temperature measure-
ment takes nominally 25.5 ms. The results of remote temperature
measurements are stored in 10-bit, twos complement format,
as illustrated in Table III. The extra resolution for the temperature
measurements is held in the Extended Resolution Register 2
(Reg. 0x77). This gives temperature readings with a resolution
of 0.25
o
C.
Table III. Temperature Data Format
*
Temperature
Digital Output (10-Bit)
128
C
1000 0000 00
125
C
1000 0011 00
100
C
1001 1100 00
75
C
1011 0101 00
50
C
1100 1110 00
25
C
1110 0111 00
10
o
C
1111 0110 00
0
C
0000 0000 00
+10.25
C
0000 1010 01
+25.5
C
0001 1001 10
+50.75
C
0011 0010 11
+75
C
0100 1011 00
+100
C
0110 0100 00
+125
C
0111 1101 00
+127
C
0111 1111 00
*Bold denotes 2 LSBs of measurement in Extended Resolution
Register 2 (Reg. 0x77) with 0.25
o
C resolution.
ADM1027
2N3904
NPN
D+
D
Figure 14a. Measuring Temperature Using an
NPN Transistor
2N3906
PNP
ADM1027
D+
D
Figure 14b. Measuring Temperature Using a
PNP Transistor
NULLING OUT TEMPERATURE ERRORS
As CPUs run faster, it is getting more difficult to avoid high
frequency clocks when routing the D/D+ traces around a system
board. Even when recommended layout guidelines are followed,
there may still be temperature errors attributed to noise being
coupled onto the D+/D lines. High frequency noise generally
has the effect of giving temperature measurements that are too
high by a constant amount. The ADM1027 has temperature
offset registers at addresses 0x70, 0x71, and 0x72 for the Remote 1,
Local, and Remote 2 temperature channels. By doing a one-time
calibration of the system, you can determine the offset caused
by system board noise and null it out using the offset registers.
The offset registers automatically add a twos complement 8-bit
reading to every temperature measurement. The LSB adds a 1
C
offset to the temperature reading so the 8-bit register effectively
allows temperature offsets of up to 127
C with a resolution of
1
C. This ensures that the readings in the temperature measure-
ment registers are as accurate as possible.
TEMPERATURE OFFSET REGISTERS
Reg. 0x70 Remote 1 Temperature Offset = 0x00 (0
C default)
Reg. 0x71 Local Temperature Offset = 0x00 (0
C default)
Reg. 0x72 Remote 2 Temperature Offset = 0x00 (0
C default)
REV. A
16
ADM1027
TEMPERATURE MEASUREMENT REGISTERS
Reg. 0x25 Remote 1 Temperature = 0x80 default
Reg. 0x26 Local Temperature = 0x80 default
Reg. 0x27 Remote 2 Temperature = 0x80 default
Reg. 0x77 Extended Resolution 2 = 0x00 default
<7:6> TDM2
= Remote 2 Temperature LSBs
<5:4> LTMP
= Local Temperature LSBs
<3:2> TDM1
= Remote 1 Temperature LSBs
TEMPERATURE MEASUREMENT LIMIT REGISTERS
Associated with each temperature measurement channel are
high and low limit registers. Exceeding the programmed high or
low limit causes the appropriate status bit to be set. Exceeding
either limit can also generate SMBALERT interrupts.
Reg. 0x4E Remote 1 Temperature Low Limit = 0x81 default
Reg. 0x4F Remote 1 Temperature High Limit = 0x7F default
Reg. 0x50 Local Temperature Low Limit = 0x81 default
Reg. 0x51 Local Temperature High Limit = 0x7F default
Reg. 0x52 Remote 2 Temperature Low Limit = 0x81 default
Reg. 0x53 Remote 2 Temperature High Limit = 0x7F default
READING TEMPERATURE FROM THE ADM1027
It is important to note that temperature can be read from the
ADM1027 as an 8-bit value (with 1
C resolution), or as a 10-
bit value (with 0.25
C resolution). If only 1C resolution is
required, the temperature readings can be read back at any time
and in no particular order.
If the 10-bit measurement is required, this involves a 2-register
read for each measurement. The extended resolution register
(Reg. 0x77) should be read first. This causes all temperature
reading registers to be frozen until all temperature reading regis-
ters have been read from. This prevents an MSB reading from
being updated while its two LSBs are being read, and vice versa.
ADDITIONAL ADC FUNCTIONS
A number of other functions are available on the ADM1027 to
offer the systems designer increased flexibility:
Turn Off Averaging
For each temperature measurement read from a value register,
16 readings have actually been made internally and the results
averaged before being placed into the value register. There may
be an instance where the user would like to take a very fast
measurement, e.g., of CPU temperature. Setting Bit 4 of Con-
figuration Register 2 (Reg. 0x73) turns averaging off. This takes
a reading every 13 ms. The measurement itself takes 4 ms.
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the
ADM1027 into single-channel ADC conversion mode. In this
mode, the ADM1027 can be made to read a single temperature
channel only. If the internal ADM1027 clock is used, the selected
input will be read every 1.4 ms. The appropriate ADC channel
is selected by writing to Bits <7:5> of TACH1 minimum high
byte register (Reg. 0x55).
Bits <7:5> Reg 0x55
Channel Selected
101
Remote 1 Temp
110
Local Temp
111
Remote 2 Temp
Configuration Register 2 (Reg. 0x73)
<4> = 1
Averaging off
<6> = 1
Single-channel convert mode
TACH1 Minimum High Byte (Reg. 0x55)
<7:5>
Selects ADC channel for single-channel convert mode
OVERTEMPERATURE EVENTS
Overtemperature events on any of the temperature channels can
be detected and dealt with automatically. Registers 0x6A to
0x6C are the THERM limits. When a temperature exceeds its
THERM limit, all fans will run at 100% duty cycle. The fans
will stay running at 100% until the temperature drops below
THERM 4
C.
FANS
THERM LIMIT
TEMP
100%
HYSTERESIS = 4 C
Figure 15. THERM Limit Operation
REV. A
ADM1027
17
SMBALERT, STATUS, AND MASK REGISTERS
SMBALERT CONFIGURATION
Pin 10 of the ADM1027 can be configured as either PWM2 or
as an SMBALERT output. The SMBALERT output may be
used to signal out-of-limit conditions as explained below. The
default state of Pin 10 is PWM2. To configure Pin 10 as
SMBALERT:
Configuration Reg. 3 (Addr = 0x78), Bit 0 = 1 = SMBALERT
Configuration Reg. 3 (Addr = 0x78), Bit 0 = 0 = PWM2 =
default
LIMIT VALUES
Associated with each measurement channel on the ADM1027
are high and low limits. These can form the basis of system
status monitoring; a status bit can be set for any out-of-limit
condition and detected by polling the device. Alternatively,
SMBALERT interrupts can be generated to flag a processor or
microcontroller of out-of-limit conditions.
8-BIT LIMITS
The following is a list of 8-bit limits on the ADM1027:
Voltage Limit Registers
Reg. 0x44 2.5 V Low Limit = 0x00 default
Reg. 0x45 2.5 V High Limit = 0xFF default
Reg. 0x46 V
CCP
Low Limit
= 0x00 default
Reg. 0x47 V
CCP
High Limit
= 0xFF default
Reg. 0x48 V
CC
Low Limit
= 0x00 default
Reg. 0x49 V
CC
High Limit
= 0xFF default
Reg. 0x4A 5 V Low Limit = 0x00 default
Reg. 0x4B 5 V High Limit = 0xFF default
Reg. 0x4C 12 V Low Limit = 0x00 default
Reg. 0x4D 12 V High Limit = 0xFF default
Temperature Limit Registers
Reg. 0x4E Remote 1 Temp Low Limit = 0x81 default
Reg. 0x4F Remote 1 Temp High Limit = 0x7F default
Reg. 0x6A Remote 1 THERM Limit = 0x64 default
Reg. 0x50 Local Temp Low Limit = 0x81 default
Reg. 0x51 Local Temp High Limit = 0x7F default
Reg. 0x6B Local THERM Limit = 0x64 default
Reg. 0x52 Remote 2 Temp Low Limit = 0x81 default
Reg. 0x53 Remote 2 Temp High Limit = 0x7F default
Reg. 0x6C Remote 2 THERM Limit = 0x64 default
16-Bit Limits
The fan TACH measurements are 16-bit results. The fan TACH
limits are also 16 bits, consisting of a high byte and low byte.
Since fans running underspeed or stalled are normally the only
conditions of interest, only high limits exist for fan TACHs.
Since fan TACH period is actually being measured, exceeding
the limit indicates a slow or stalled fan.
Fan Limit Registers
Reg. 0x54 TACH1 Minimum Low Byte = 0xFF default
Reg. 0x55 TACH1 Minimum High Byte = 0xFF default
Reg. 0x56 TACH2 Minimum Low Byte = 0xFF default
Reg. 0x57 TACH2 Minimum High Byte = 0xFF default
Reg. 0x58 TACH3 Minimum Low Byte = 0xFF default
Reg. 0x59 TACH3 Minimum High Byte = 0xFF default
Reg. 0x5A TACH4 Minimum Low Byte = 0xFF default
Reg. 0x5B TACH4 Minimum High Byte = 0xFF default
OUT-OF-LIMIT COMPARISONS
The ADM1027 will measure all parameters in round-robin format
and set the appropriate status bit for out-of-limit conditions.
Comparisons are done differently depending on whether the
measured value is being compared to a high or low limit.
HIGH LIMIT: > COMPARISON PERFORMED
LOW LIMIT: < OR = COMPARISON PERFORMED
REV. A
18
ADM1027
ANALOG MONITORING CYCLE TIME
The analog monitoring cycle begins when a 1 is written to the
start bit (Bit 0) of Configuration Register 1(Reg. 0x40). The
ADC measures each analog input in turn and as each mea-
surement is completed, the result is automatically stored in the
appropriate value register. This round-robin monitoring cycle
continues unless disabled by writing a 0 to Bit 0 of Configura-
tion Register 1.
Since the ADC will normally be left to free-run in this manner,
the time taken to monitor all the analog inputs will normally not
be of interest as the most recently measured value of any input
can be read out at any time.
For applications where the monitoring cycle time is important,
it can easily be calculated.
The total number of channels measured is
Four dedicated supply voltage inputs
3.3 V
STBY
or 5 V supply (V
CC
pin)
Local temperature
Two remote temperatures
As mentioned previously, the ADC performs round-robin con-
versions and takes 11.38 ms for each voltage measurement,
12 ms for a local temperature reading, and 25.5 ms for a remote
temperature reading.
The total monitoring cycle time for averaged voltage and tem-
perature monitoring is therefore nominally
(5
11.38) + 12 + (2 25.5) = 120 ms
Fan TACH measurements are made in parallel and are not
synchronized with the analog measurements in any way.
STATUS REGISTERS
The results of limit comparisons are stored in Status Registers 1
and 2. The status register bit for each channel reflects the status of
the last measurement and limit comparison on that channel.
If a measurement is within limits, the corresponding status
register bit will be cleared to 0. If the measurement is out-of-limits,
the corresponding status register bit will be set to 1.
The state of the various measurement channels may be polled by
reading the status registers over the serial bus. When 1, Bit 7
(OOL) of Status Register 1 (Reg. 0x41) means that an out-of-
limit event has been flagged in Status Register 2. This means that
the user need read only Status Register 2 when this bit is set.
Alternatively, Pin 10 can be configured as an
SMBALERT output.
This will automatically notify the system supervisor of an
out-of-limit condition. Reading the status registers clears the
appropriate status bit as long as the error condition that caused
the interrupt has cleared. Status register bits are "sticky."
Whenever a status bit gets set, indicating an out-of-limit
condition, it will remain set even if the event that caused it has
gone away (until read). The only way to clear the status bit is to
read the status register after the event has gone away. Interrupt
status mask registers (Reg. 0x74, 0x75) allow individual inter-
rupt sources to be masked from causing an
SMBALERT.
However, if one of these masked interrupt sources goes out-
of-limit, its associated status bit will get set in the interrupt
status registers.
STATUS REGISTER 1 (REG. 0x41)
Bit 7 (OOL) = 1, denotes a bit in Status Register 2 is set and
Status Register 2 should be read.
Bit 6 (R2T) = 1, Remote 2 temp high or low limit has been
exceeded.
Bit 5 (LT) = 1, Local temp high or low limit has been exceeded.
Bit 4 (R1T) = 1, Remote 1 temp high or low limit has been
exceeded.
Bit 3 (5 V) = 1, 5 V high or low limit has been exceeded.
Bit 2 (V
CC
) = 1, V
CC
high or low limit has been exceeded.
Bit 1 (V
CCP
) = 1, V
CCP
high or low limit has been exceeded.
Bit 0 (2.5 V) = 1, 2.5 V high or low limit has been exceeded.
STATUS REGISTER 2 (REG. 0x42)
Bit 7 (D2) = 1, indicates an open or short on D2+/D2 inputs.
Bit 6 (D1) = 1, indicates an open or short on D2+/D2 inputs.
Bit 5 (FAN4) = 1, indicates Fan 4 has dropped below mini-
mum speed.
Bit 4 (FAN3) = 1, indicates Fan 3 has dropped below mini-
mum speed.
Bit 3 (FAN2) = 1, indicates Fan 2 has dropped below mini-
mum speed.
Bit 2 (FAN1) = 1, indicates Fan 1 has dropped below mini-
mum speed.
Bit 1 (OVT) = 1, indicates that a THERM overtemperature
limit has been exceeded.
Bit 0 (12 V) = 1, 12 V high or low limit has been exceeded.
REV. A
ADM1027
19
SMBALERT INTERRUPT BEHAVIOR
The ADM1027 can be polled for status, or an
SMBALERT
interrupt can be generated for out-of-limit conditions. It is
important to note how the
SMBALERT output and status bits
behave when writing interrupt handler software.
STICKY
STATUS
BIT
HIGH LIMIT
TEMPERATURE
SMBALERT
CLEARED ON READ
(TEMP BELOW LIMIT)
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
Figure 16.
SMBALERT and Status Bit Behavior
Figure 16 shows how the
SMBALERT output and sticky status
bits behave. Once a limit is exceeded, the corresponding status
bit is set to 1. The status bit remains set until the error condition
subsides and the status register is read. The status bits are referred
to as sticky since they remain set until read by software. This
ensures that an out-of-limit event cannot be missed if software
is polling the device periodically. Note that the
SMBALERT
output remains low for the entire duration that a reading is
out-of-limit and until the status register has been read. This has
implications on how software handles the interrupt.
HANDLING
SMBALERT INTERRUPTS
To prevent the system from being tied up servicing interrupts,
it is recommend to handle the
SMBALERT interrupt as follows:
1. Detect the
SMBALERT assertion.
2. Enter the interrupt handler.
3. Read the status registers to identify the interrupt source.
4. Mask the interrupt source by setting the appropriate mask bit
in the interrupt mask registers (Reg. 0x74, 0x75).
5. Take the appropriate action for a given interrupt source.
6. Exit the interrupt handler.
7. Periodically poll the status registers. If the interrupt status bit
has cleared, reset the corresponding interrupt mask bit to 0.
This will cause the
SMBALERT output and status bits to
behave as shown in Figure 17.
STICKY
STATUS
BIT
HIGH LIMIT
TEMPERATURE
SMBALERT
CLEARED ON READ
(TEMP BELOW LIMIT)
TEMP BACK IN LIMIT
(STATUS BIT STAYS SET)
INTERRUPT
MASK BIT SET
INTERRUPT MASK
BIT CLEARED
(
SMBALERT REARMED)
Figure 17. How Masking the Interrupt Source
Affects
SMBALERT Output
MASKING INTERRUPT SOURCES
Interrupt Mask Registers 1 and 2 are located at Addresses 0x74
and 0x75. These allow individual interrupt sources to be masked
out to prevent
SMBALERT interrupts. Note that masking an
interrupt source prevents only the
SMBALERT output from
being asserted; the appropriate status bit will be set as normal.
INTERRUPT MASK REGISTER 1 (REG. 0x74)
Bit 7 (OOL) = 1, set this bit to 1 to allow masking of interrupts
by Status Register 2. If this bit = 0, then setting a bit in Mask
Register 2 to 1 will have no effect.
Bit 6 (R2T) = 1, masks
SMBALERT for Remote 2 temperature.
Bit 5 (LT) = 1, masks
SMBALERT for local temperature.
Bit 4 (R1T) = 1, masks
SMBALERT for Remote 1 temperature.
Bit 3 (5 V) = 1, masks
SMBALERT for 5 V channel.
Bit 2 (V
CC
) = 1, masks
SMBALERT for V
CC
channel.
Bit 1 (V
CCP
) = 1, masks
SMBALERT for V
CCP
channel.
Bit 0 (2.5 V) = 1, masks
SMBALERT for 2.5 V channel.
INTERRUPT MASK REGISTER 2 (REG. 0x75)
Bit 7 (D2) = 1, masks
SMBALERT for Diode 2 errors.
Bit 6 (D1) = 1, masks
SMBALERT for Diode 1 errors.
Bit 5 (FAN4) = 1, masks
SMBALERT for Fan 4.
Bit 4 (FAN3) = 1, masks
SMBALERT for Fan 3.
Bit 3 (FAN2) = 1, masks
SMBALERT for Fan 2.
Bit 2 (FAN1) = 1, masks
SMBALERT for Fan 1.
Bit 1 (OVT) = 1, masks
SMBALERT for overtemperature
(exceeding THERM limits).
Bit 0 (12 V) = 1, masks
SMBALERT for 12 V channel.
REV. A
20
ADM1027
FAN DRIVE CIRCUITRY
Fan Drive Using PWM Control
The ADM1027 uses Pulsewidth Modulation (PWM) to control
fan speed. This relies on varying the duty cycle (or on/off ratio)
of a square wave applied to the fan to vary the fan speed. The
external circuitry required to drive a fan using PWM control is
extremely simple. A single NMOSFET is the only drive device
required. The specifications of the MOSFET depend on the
maximum current required by the fan being driven. Typical
notebook fans draw a nominal 170 mA, so SOT devices can be
used where board space is a concern. In desktops, fans can
typically draw 250 mA to 300 mA each. If you drive several fans
in parallel from a single PWM output or drive larger server fans,
the MOSFET will need to handle the higher current require-
ments. The only other stipulation is that the MOSFET should
have a gate voltage drive, V
GS
< 3.3 V for direct interfacing to
the PWM_OUT pin. V
GS
can be greater than 3.3 V as long as
the pull-up on the gate is tied to 5 V. The MOSFET should
also have a low on resistance to ensure that there is not signifi-
cant voltage drop across the FET. This would reduce the
voltage applied across the fan and thus the maximum operating
speed of the fan.
Figure 18 shows how a 3-wire fan may be driven using PWM
control.
ADM1027
TACH/AIN
PWM
4.7k
10k
10k
10k
3.3V
12V
12V
12V
FAN
Q1
NDT3055L
Figure 18. Driving a 3-Wire Fan Using an
N-Channel MOSFET
Figure 18 uses a 10 k
W pull-up resistor for the TACH signal.
This assumes that the TACH signal is open-collector from the
fan. In all cases, the TACH signal from the fan must be kept
below 5 V maximum to prevent damaging the ADM1027. If in
doubt as to whether the fan used has an open-collector or totem
pole TACH output, use one of the input signal conditioning
circuits shown in the Fan Speed Measurement section.
Figure 19 shows a fan drive circuit using an NPN transistor
such as a general-purpose MMBT2222. While these devices are
inexpensive, they tend to have much lower current handling
capabilities and higher on resistance than MOSFETs. When
choosing a transistor, care should be taken to ensure that it
meets the fan's current requirements. Ensure that the base
resistor is chosen such that the transistor is saturated when the
fan is powered on.
ADM1027
TACH/AIN
PWM
4.7k
10k
10k
10k
3.3V
12V
12V
12V
FAN
Q1
MMBT2222
Figure 19. Driving a 3-Wire Fan Using an NPN Transistor
REV. A
ADM1027
21
ADM1027
PWM3
2.2k
10k
3.3V
Q1
MMBT3904
3.3V
10
TACH3
Q2
MMBT2222
10
TACH4
12V
Q3
MMBT2222
Figure 20. Interfacing Two Fans in Parallel to the PWM3 Output Using Low Cost NPN Transistors
ADM1027
TACH4
10k
TYPICAL
3.3V
TACH
TACH3
10k
TYPICAL
3.3V
PWM3
10k
TYPICAL
3.3V
+V
Q1
NDT3055L
5V OR 12V
FAN
TACH
5V OR 12V
FAN
+V
Figure 21. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET
Driving 2 Fans From PWM3
Note that the ADM1027 has four TACH inputs available for
fan speed measurement, but only three PWM drive outputs. If a
fourth fan is being used in the system, it should be driven from
the PWM3 output in parallel with the third fan. Figure 20
shows how to drive two fans in parallel using low cost NPN
transistors. Figure 21 is the equivalent circuit using the
NDT3055L MOSFET. Note that since the MOSFET can
handle up to 3.5 A, it is simply a matter of connecting another
fan directly in parallel with the first.
Care should be taken in designing drive circuits with transistors
and FETs to ensure that the PWM pins are not required to
source current, and that they sink less than the 8 mA max cur-
rent specified on the data sheet.
REV. A
22
ADM1027
Driving 2-Wire Fans
Figure 22 shows how a 2-wire fan may be connected to the
ADM1027. This circuit allows the speed of a 2-wire fan to be
measured even though the fan has no dedicated TACH signal.
A series resistor, R
SENSE
, in the fan circuit converts the fan
commutation pulses into a voltage. This is ac-coupled into the
ADM1027 through the 0.01 F capacitor. On-chip signal con-
ditioning allows accurate monitoring of fan speed. For fans
drawing approximately 200 mA, a 2
W R
SENSE
value is suitable.
For fans that draw more current, such as larger desktop or
server fans, R
SENSE
may be reduced. The smaller R
SENSE
is the
better, since more voltage will be developed across the fan, and
the fan will spin faster. Figure 23 shows a typical plot of the
sensing waveform at a TACH/AIN pin. The most important
thing is that the negative going spikes are more than 250 mV in
amplitude. This allows fan speed to be reliably determined.
ADM1027
TACH/AIN
PWM
10k
TYPICAL
3.3V
+V
Q1
NDT3055L
5V OR 12V
FAN
R
SENSE
2
TYPICAL
0.01 F
Figure 22. Driving a 2-Wire Fan
1
Ch1
4
100mV
Ch2 5.00mV
M 4.00ms A Ch1
2.00mV
Ch3 50.0mV
Ch4 50.0mV
T
: +250mV
@: 258mV
1.00000ms
T
Tek PreVu
[
]
T
Figure 23. Fan Speed Sensing Waveform at
TACH/AIN Pin
Laying Out for 2-Wire and 3-Wire Fans
Figure 24 shows how to lay out a common circuit arrangement
for 2-wire and 3-wire fans. Some components will not be popu-
lated depending on whether a 2-wire or 3-wire fan is being used.
3.3V OR 5V
TACH/AIN
PWM
12V OR 5V
Q1
MMBT2222
R4
R5
R3
C1
R2
R1
FOR 3-WIRE FANS:
POPULATE R1, R2, R3
R4 = 0
C1 = UNPOPULATED
FOR 2-WIRE FANS:
POPULATE R4, C1
R1, R2, R3 UNPOPULATED
Figure 24. Planning for 2-Wire or 3-Wire Fans on a PCB
REV. A
ADM1027
23
FAN SPEED MEASUREMENTS
TACH Inputs
Pins 11, 12, 9, and 14 are open-drain TACH inputs intended
for fan speed measurement.
Signal conditioning in the ADM1027 accommodates the slow
rise and fall times typical of fan tachometer outputs. The maxi-
mum input signal range is 0 V to 5 V, even where V
CC
is less
than 5 V. In the event that these inputs are supplied from fan
outputs that exceed 0 V to 5 V, either resistive attenuation of
the fan signal or diode clamping must be included to keep
inputs within an acceptable range.
Figures 25a to 25d show circuits for most common fan TACH
outputs. If the fan TACH output has a resistive pull-up to V
CC
, it
can be connected directly to the fan input, as shown in Figure 25a.
5V OR 12V
ADM1027
FAN SPEED
COUNTER
TACH X
TACHO
OUTPUT
PULL-UP
4.7k
TYP
V
CC
FAN
Figure 25a. Fan With TACH Pull-Up to +V
CC
If the fan output has a resistive pull-up to 12 V (or other voltage
greater than 5 V), then the fan output can be clamped with a
Zener diode, as shown in Figure 25b. The Zener diode voltage
should be chosen so that it is greater than V
IH
of the TACH
input but less than 5 V, allowing for the voltage tolerance of the
Zener. A value of between 3 V and 5 V is suitable.
5V OR 12V
ADM1027
FAN SPEED
COUNTER
TACH X
TACHO
OUTPUT
PULL-UP
4.7k
TYP
V
CC
FAN
ZD1*
*CHOOSE ZD1 VOLTAGE APPROX 0.8 V
CC
Figure 25b. Fan with TACH Pull-Up to Voltage
> 5 V (e.g., 12 V) Clamped with Zener Diode
If the fan has a strong pull-up (less than 1 k ) to 12 V, or a
totem-pole output, then a series resistor can be added to limit
the Zener current, as shown in Figure 25c. Alternatively, a
resistive attenuator may be used, as shown in Figure 25d.
R1 and R2 should be chosen such that
2
2
1
2
5
V
V
R
R
R
R
V
PULLUP
PULLUP
<
+
+
(
)
>
The fan inputs have an input resistance of nominally 160 k
W to
ground; this should be taken into account when calculating
resistor values.
With a pull-up voltage of 12 V and pull-up resistor less than
1 k
W, suitable values for R1 and R2 would be 100 kW and
47 k
W. This will give a high input voltage of 3.83 V.
5V OR 12V
ADM1027
FAN SPEED
COUNTER
TACH X
TACHO
OUTPUT
PULL-UP TYP
<1k
OR
TOTEM POLE
V
CC
FAN
ZD1*
*CHOOSE ZD1 VOLTAGE APPROX 0.8 V
CC
R1
10k
Figure 25c. Fan with Strong TACH Pull-Up to > V
CC
or
Totem-Pole Output, Clamped with Zener and Resistor
5V OR 12V
ADM1027
FAN SPEED
COUNTER
TACH X
TACHO
OUTPUT
PULL-UP TYP
<1k
V
CC
FAN
R2*
*SEE TEXT
R1*
Figure 25d. Fan with Strong TACH Pull-Up to > V
CC
or Totem-Pole Output, Attenuated with R1/R2
Fan Speed Measurement
The fan counter does not count the fan TACH output pulses
directly because the fan speed may be less than 1000 RPM and
it would take several seconds to accumulate a reasonably large
and accurate count. Instead, the period of the fan revolution is
measured by gating an on-chip 90 kHz oscillator into the input
of a 16-bit counter for N periods of the fan TACHO output
(Figure 26), so the accumulated count is actually proportional
to the fan tachometer period and inversely proportional to the
fan speed.
1
2
3
4
CLOCK
PWM
TACH
Figure 26. Fan Speed Measurement
N, the number of pulses counted, is determined by the settings
of Register 0x7B (fan pulses per revolution register). This register
contains two bits for each fan, allowing 1, 2 (default), 3, or 4
TACH pulses to be counted.
REV. A
24
ADM1027
Fan Speed Measurement Registers
The fan tachometer readings are 16-bit values consisting of a
2-byte read from the ADM1027.
Reg. 0x28 TACH1 Low Byte = 0x00 default
Reg. 0x29 TACH1 High Byte = 0x00 default
Reg. 0x2A TACH2 Low Byte = 0x00 default
Reg. 0x2B TACH2 High Byte = 0x00 default
Reg. 0x2C TACH3 Low Byte = 0x00 default
Reg. 0x2D TACH3 High Byte = 0x00 default
Reg. 0x2E TACH4 Low Byte = 0x00 default
Reg. 0x2F TACH4 High Byte = 0x00 default
Reading Fan Speed From the ADM1027
If fan speeds are being measured, this involves a 2-register read
for each measurement. The low byte should be read first. This
causes the high byte to be frozen until both high and low byte
registers have been read from. This prevents erroneous TACH
readings.
The fan tachometer reading registers report back the number of
11.11 s period clocks (90 kHz oscillator) gated to the fan
speed counter, from the rising edge of the first fan TACH pulse
to the rising edge of the third fan TACH pulse (assuming two
pulses per revolution are being counted). Since the device is
essentially measuring the fan TACH period, the higher the
count value, the slower the fan is actually running. A 16-bit fan
tachometer reading of 0xFFFF indicates that the fan either has
stalled or is running very slowly (< 100 RPM).
HIGH LIMIT: > COMPARISON PERFORMED
Since actual fan TACH period is being measured, exceeding a
fan TACH limit by 1 will set the appropriate status bit and can
be used to generate an
SMBALERT.
Fan Tach Limit Registers
The fan TACH limit registers are 16-bit values consisting of
two bytes.
Reg. 0x54 TACH1 Minimum Low Byte = 0xFF default
Reg. 0x55 TACH1 Minimum High Byte = 0xFF default
Reg. 0x56 TACH2 Minimum Low Byte = 0xFF default
Reg. 0x57 TACH2 Minimum High Byte = 0xFF default
Reg. 0x58 TACH3 Minimum Low Byte = 0xFF default
Reg. 0x59 TACH3 Minimum High Byte = 0xFF default
Reg. 0x5A TACH4 Minimum Low Byte = 0xFF default
Reg. 0x5B TACH4 Minimum High Byte = 0xFF default
Fan Speed Measurement Rate
The fan TACH readings are normally updated once every second.
The fast bit (Bit 3) of Configuration Register 3 (Reg. 0x78),
when set, updates the fan TACH readings every 250 ms.
If any of the fans are not being driven by a PWM channel but
are powered directly from 5 V or 12 V, their associated dc bit in
Configuration Register 3 should be set. This allows TACH
readings to be taken on a continuous basis for fans connected
directly to a dc source.
Calculating Fan Speed
Assuming a fan with 2 pulses/revolution (and 2 pulses/rev being
measured), fan speed is calculated by:
Fan Speed RPM
Fan Tach Reading
(
)
=
(
)
90 000
60
,
where Fan Tach Reading = 16-bit fan tachometer reading.
Example:
TACH1 high byte (Reg. 0x29) = 0x17
TACH1 low byte (Reg. 0x28) = 0xFF
What is Fan 1 speed in RPM?
Fan 1 TACH reading = 0x17FF = 6143 decimal
RPM = (f
60)/fan 1 TACH reading
RPM = (90000
60)/6143
Fan Speed = 879 RPM
FAN PULSES PER REVOLUTION
Different fan models can output either 1, 2, 3, or 4 TACH
pulses per revolution. Once the number of fan TACH pulses
has been determined, it can be programmed into the fan pulses
per revolution register (Reg. 0x7B) for each fan. Alternatively,
this register can be used to determine the number or pulses/
revolution output by a given fan. By plotting fan speed measure-
ments at 100% speed with different pulses/rev setting, the
smoothest graph with the lowest ripple determines the correct
pulses/rev value.
Fan Pulses Per Revolution Register
<1:0> FAN1 default = 2 pulses/rev
<3:2> FAN2 default = 2 pulses/rev
<5:4> FAN3 default = 2 pulses/rev
<7:6> FAN4 default = 2 pulses/rev
00 = 1 pulse/rev
01 = 2 pulses/rev
10 = 3 pulses/rev
11 = 4 pulses/rev
REV. A
ADM1027
25
2-Wire Fan Speed Measurements
The ADM1027 is capable of measuring the speed of 2-wire
fans, i.e., fans without TACH outputs. To do this, the fan must
be interfaced as shown in the Fan Drive Circuitry section of the
data sheet. In this case, the TACH inputs need to be repro-
grammed as analog inputs, AIN.
CONFIGURATION REGISTER 2 (REG. 0x73)
Bit 3 (AIN4) = 1, Pin 14 is reconfigured to measure the speed
of a 2-wire fan using an external sensing resistor and coupling
capacitor.
Bit 2 (AIN3) = 1, Pin 9 is reconfigured to measure the speed of
a 2-wire fan using an external sensing resistor and coupling
capacitor.
Bit 1 (AIN2) = 1, Pin 12 is reconfigured to measure the speed
of a 2-wire fan using an external sensing resistor and coupling
capacitor.
Bit 0 (AIN1) = 1, Pin 11 is reconfigured to measure the speed
of a 2-wire fan using an external sensing resistor and coupling
capacitor.
FAN SPIN-UP
The ADM1027 has a unique fan spin-up function. It will spin
the fan at 100% PWM duty cycle until two TACH pulses are
detected on the TACH input. Once two pulses have been
detected, the PWM duty cycle will go to the expected running
value, e.g., 33%. The advantage of this is that fans have dif-
ferent spin-up characteristics and will take different times to
overcome inertia. The ADM1027 just runs the fans fast enough
to overcome inertia and will be quieter on spin-up than fans
programmed to spin up for a given spin-up time.
FAN START-UP TIMEOUT
To prevent false interrupts being generated as a fan spins up
(since it is below running speed), the ADM1027 includes a fan
start-up timeout function. This is the time limit allowed for two
TACH pulses to be detected on spin-up. For example, if 2
seconds fan start-up timeout is chosen, and no TACH pulses
occur within 2 seconds of the start of spin-up, a fan fault is
detected and flagged in the interrupt status registers.
PWM1 CONFIGURATION (REG. 0x5C)
<2:0> SPIN
These bits control the start-up timeout for
PWM1.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
PWM2 CONFIGURATION (REG. 0x5D)
<2:0> SPIN
These bits control the start-up timeout for
PWM2.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
PWM3 CONFIGURATION (REG. 0x5E)
<2:0> SPIN
These bits control the start-up timeout for
PWM3.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
Disabling Fan Start-Up Timeout
Although fan start-up makes fan spin-ups much quieter than
fixed-time spin-ups, the option is there to use fixed spin-up times.
Bit 5 (FSPDIS) = 1 in Configuration Register 1 (Reg. 0x40)
disables the spin-up for two TACH pulses. Instead, the fan will
spin up for the fixed time as selected in registers 0x5C to 0x5E.
REV. A
26
ADM1027
MANUAL FAN SPEED CONTROL MODE
PWM Logic State
The PWM outputs can be programmed to be high for 100%
duty cycle (noninverted) or low for 100% duty cycle (inverted).
PWM1 Configuration (Reg. 0x5C)
<4> INV
0 = logic high for 100% PWM duty cycle
1 = logic low for 100% PWM duty cycle
PWM2 Configuration (Reg. 0x5D)
<4> INV
0 = logic high for 100% PWM duty cycle
1 = logic low for 100% PWM duty cycle
PWM3 Configuration (Reg. 0x5E)
<4> INV
0 = logic high for 100% PWM duty cycle
1 = logic low for 100% PWM duty cycle
PWM Drive Frequency
The PWM drive frequency can be adjusted for the application.
Registers 0x5F to 0x61 configure the PWM frequency for
PWM1 to PWM3, respectively.
PWM1 FREQUENCY REGISTERS (REG. 0x5F to 0x61)
<2:0> FREQ
000 = 11.0 Hz
001 = 14.7 Hz
010 = 22.1 Hz
011 = 29.4 Hz
100 = 35.3 Hz (default)
101 = 44.1 Hz
110 = 58.8 Hz
111 = 88.2 Hz
Manual Fan Speed Control
The ADM1027 allows the duty cycle of any PWM output to be
manually adjusted. This can be useful if you want to change fan
speed in software or want to adjust PWM duty cycle output for
test purposes. Bits <7:5> of Registers 0x5C to 0x5E (PWM
configuration) control the behavior of each PWM output.
PWM CONFIGURATION (REG. 0x5C to 0x5E)
<7:5> BHVR 111 = Manual Mode
Once under manual control, each PWM output may be manually
updated by writing to Registers 0x30 to 0x32 (PWMx current
duty cycle registers).
Programming the PWM
Current Duty Cycle Registers
The PWM
current duty cycle registers are 8-bit registers that
allow the PWM duty cycle for each output to be set anywhere
from 0% to 100%. This allows the PWM duty cycle to be set in
steps of 0.39%.
The value to be programmed into the PWM
MIN
register is
given by
Value decimal
PWM
MIN
(
)
=
0 39
.
Example 1: for a PWM duty cycle of 50%,
Value (decimal) = 50/0.39 = 128 decimal
Value = 128 decimal or 80 hex.
Example 2: for a PWM duty cycle of 33%,
Value (decimal) = 33/0.39 = 85 decimal
Value = 85 decimal or 54 hex.
PWM Duty Cycle Registers
Reg. 0x30 PWM1 Duty Cycle = 0xFF (100% default)
Reg. 0x31 PWM2 Duty Cycle = 0xFF (100% default)
Reg. 0x32 PWM3 Duty Cycle = 0xFF (100% default)
By reading the PWMx current duty cycle registers, you can keep
track of the current duty cycle on each PWM output, even when
the fans are running in automatic fan speed control mode or
acoustic enhancement mode.
REV. A
ADM1027
27
AUTOMATIC FAN SPEED CONTROL MODE
The ADM1027 has a local temperature sensor and two remote
temperature channels that may be connected to an on-chip
diode-connected transistor on a CPU. These three temperature
channels may be used as the basis for automatic fan speed control
to drive fans using pulsewidth modulation (PWM). In general,
the greater the number of fans in a system, the better the cooling,
but to the detriment of system acoustics. Automatic fan speed
control reduces acoustic noise by optimizing fan speed according
to measured temperature. Reducing fan speed can also decrease
system current consumption. The automatic fan speed control
mode is very flexible, owing to the number of programmable param-
eters, including T
MIN
and T
RANGE
, as discussed in detail later.
The T
MIN
and T
RANGE
values chosen for a given fan are critical,
since these define the thermal characteristics of the system. The
thermal validation of the system is one of the most important
steps of the design process, so these values should be carefully
selected.
The aim of this section is not only to provide the system designer
with an understanding of the automatic fan control loop, but also
to provide step-by-step guidance as to how to most effectively
evaluate and select the critical system parameters. To optimize
the system characteristics, the designer needs to give some fore-
thought to how the system will be configured, e.g., the number
of fans, where they are located, and what temperatures are being
measured in the particular system. The mechanical or thermal
engineer who is tasked with the actual system evaluation should
also be involved at the beginning of the process.
Automatic Fan Control Overview
Figure 27 gives a top-level overview of the automatic fan control
circuitry on the ADM1027. From a systems-level perspective,
up to three system temperatures can be monitored and used to
control three PWM outputs. The three PWM outputs can be
used to control up to four fans. The ADM1027 allows the speed
of four fans to be monitored. The right side of the block diagram
shows controls that are fan-specific. The designer has control
over individual parameters such as minimum PWM duty cycle,
fan speed failure thresholds, and even ramp control of the PWM
outputs. This ultimately allows graceful fan speed changes that
are less perceptible to the system user.
TACHOMETER 1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER 3
AND 4
MEASUREMENT
PWM
GENERATOR
PWM
CONFIG
PWM
GENERATOR
PWM
CONFIG
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
PWM
GENERATOR
PWM
CONFIG
PWM
MIN
PWM
MIN
PWM
MIN
MUX
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
PWM1
PWM2
PWM3
REMOTE 1
TEMP
LOCAL
TEMP
REMOTE 2
TEMP
Figure 27. Automatic Fan Control Block Diagram
REV. A
28
ADM1027
Step 1
Determine the Hardware Configuration
Essentially this means choosing whether to use Pin 10 as a PWM2
output or as an SMBALERT output and deciding which SMBus
address is to be used. To set Pin 10 as SMBALERT, set Bit 0
of Configuration Register 3 (Addr = 0x78) equal to 1. The
default state is PWM2, where this bit equals 0.
It also refers to the layout recommendations of the ADM1027
on a motherboard, for example.
ADM1027 Placement Considerations
Motherboards are electrically noisy environments, and care must
be taken to protect the analog inputs from noise, particularly the
D+/D lines of a remote diode sensor. The following precautions
should be taken:
1. Place the ADM1027 as close as possible to the remote sensing
diode. Provided that the worst noise sources such as clocks
and data/address buses are avoided, this distance can be
4 inches to 8 inches.
2. Route the D+ and D tracks close together, in parallel, with
grounded guard tracks on each side. Provide a ground plane
under the tracks if possible. Do NOT run the D+/D lines in
different directions.
3. Use wide tracks to minimize inductance and reduce noise
pickup. A 10 mil track minimum width and spacing is
recommended.
4. Try to minimize the number of copper/solder joints, which
can cause thermocouple effects. Where copper/solder joints
are used, make sure that they are in both the D+ and D
path and at the same temperature. Avoid routing D+/D
on multiple layers or through vias if possible. These increase
series resistance that will cause temperature error.
5. Place a 0.1
mF supply bypass capacitor close to the ADM1027.
6. If the distance to the remote sensor is more than 8 inches,
the use of shielded twisted pair cable is recommended. This
will work up to 100 feet. Connect the twisted pair to D+/D
and the shield to GND close to the ADM1027. Leave the
remote end of the shield unconnected to avoid ground loops.
Because the measurement technique uses switched current
sources, excessive cable (adds resistance) and/or filter capacitance
can affect the measurement. A 1
W series resistance introduces
about 0.8
o
C error.
REV. A
ADM1027
29
Step 2
Configuring the Mux: Which Temperature Controls Which Fan?
Having decided on the system hardware configuration, the fans
can be assigned to particular temperature channels. Not only
can fans be assigned to individual channels, but how a fan
behaves is configurable. For example, fans can run under
automatic fan control, manually (software control), or can run
at the fastest speed calculated by multiple temperature channels.
The MUX is the bridge between temperature measurement
channels and the three PWM outputs.
Bits <7:5> (BHVR bits) of Registers 0x5C, 0x5D, and 0x5E
(PWM configuration registers) control the behavior of the fans
connected to the PWM1, PWM2, and PWM3 outputs. The
values selected for these bits determine how the MUX connects
a temperature measurement channel to a PWM output.
Automatic Fan Control Mux Options
<7:5> (BHVR) REGISTERS 0x5C, 0x5D, 0x5E
000 = Remote 1 temp controls PWMx
001 = Local temp controls PWMx
010 = Remote 2 temp controls PWMx
101 = Fastest speed calculated by local and remote 2 temp
controls PWMx
110 = Fastest speed calculated by all three temperature channels
controls PWMx
The fastest speed calculated options refer to the ability to con-
trol one PWM output based on multiple temperature channels.
While the thermal characteristics of the three temperature zones
can be set up differently, they can drive a single fan. An example
would be if the fan turns on when Remote 1 temp exceeds 60
C
or local temp exceeds 45
C.
Other Mux Options
<7:5> (BHVR) REGISTERS
0x5C, 0x5D, 0x5E
011 = PWMx runs full-speed (default).
100 = PWMx disabled.
111 = Manual Mode. PWMx is run under software control. In
this mode, PWM duty cycle registers (Reg. 0x30 to 0x32) are
writable and control the PWM outputs.
REMOTE 1 =
AMBIENT TEMP
LOCAL =
VRM TEMP
REMOTE 2 =
CPU TEMP
PWM1
TACH1
CPU
FANSINK
FRONT
CHASSIS
REAR
CHASSIS
PWM3
TACH3
PWM2
TACH2
MUX
TACHOMETER 1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETERS 3
AND 4
MEASUREMENT
PWM
GENERATOR
PWM
GENERATOR
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
PWM
GENERATOR
PWM
CONFIG
PWM
MIN
MUX
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
PWM
MIN
PWM
MIN
PWM
CONFIG
PWM
CONFIG
Figure 28. Assigning Temperature Channels to Fan Channels
REV. A
30
ADM1027
Step 3
Determine T
MIN
Setting for Each Thermal Channel
T
MIN
is the temperature at which the fans will start to turn on
under automatic fan control. The speed at which the fan runs
at T
MIN
is programmed later. The T
MIN
values chosen will be
temperature channel specific, e.g., 25
C for ambient channel,
30
C for VRM temperature, and 40C for processor temperature.
T
MIN
is an 8-bit twos complement value that can be pro-
grammed in 1
C increments. There is a T
MIN
register associated
with each temperature measurement channel, Remote 1, Local
and Remote 2 Temp. Once the T
MIN
value is exceeded, the fan
turns on and runs at minimum PWM duty cycle. The fan will
turn off once temperature has dropped below T
MIN
T
HYST
(detailed later).
To overcome fan inertia, the fan is spun up until two valid TACH
rising edges are counted. See the Fan Start-Up Timeout section
for more details. In some cases, primarily for psycho-acoustic
reasons, it is desirable that the fan never switches off below T
MIN
.
Bits <7:5> of Enhance Acoustics Register 1 (Reg. 0x62), when
set, keep the fans running at PWM minimum duty cycle should
the temperature be below T
MIN
.
T
MIN
Registers
Reg. 0x67 Remote 1 Temperature T
MIN
= 0x5A (90
C default)
Reg. 0x68 Local Temperature T
MIN
= 0x5A (90
C default)
Reg. 0x69 Remote 2 Temperature T
MIN
= 0x5A (90
C default)
Enhance Acoustics Reg 1 (Reg. 0x62)
Bit 7 (MIN3) = 0, PWM3 is OFF (0% PWM duty cycle) when
temperature is below T
MIN
T
HYST
.
Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle
below T
MIN
T
HYST
.
Bit 6 (MIN2) = 0, PWM2 is OFF (0% PWM duty cycle) when
temperature is below T
MIN
T
HYST
.
Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle
below T
MIN
T
HYST
.
Bit 5 (MIN1) = 0, PWM1 is OFF (0% PWM duty cycle) when
temperature is below T
MIN
T
HYST
.
Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle
below T
MIN
T
HYST
.
T
MIN
0%
100%
PWM DUTY CYCLE
TACHOMETER 1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETERS 3
AND 4
MEASUREMENT
PWM
GENERATOR
PWM
GENERATOR
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT
PWM
GENERATOR
PWM
CONFIG
PWM
MIN
MUX
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
PWM
MIN
PWM
MIN
PWM
CONFIG
PWM
CONFIG
REMOTE 1 =
AMBIENT TEMP
LOCAL =
VRM TEMP
REMOTE 2 =
CPU TEMP
PWM1
TACH1
CPU
FANSINK
FRONT
CHASSIS
REAR
CHASSIS
PWM3
TACH3
PWM2
TACH2
Figure 29. Understanding T
MIN
Parameter
REV. A
ADM1027
31
Step 4
Determine PWM
MIN
for Each PWM (Fan) Output
PWM
MIN
is the minimum PWM duty cycle that each fan in the
system will run at. It is also the start speed for each fan under
automatic fan control once the temperature rises above T
MIN
.
For maximum system acoustic benefit, PWM
MIN
should be as
low as possible. Starting the fans at higher speeds than necessary
will merely make the system louder than needed. Depending on
the fan used, the PWM
MIN
setting should be in the range 20%
to 33% duty cycle. This value can be found through
fan validation.
TEMPERATURE
T
MIN
100%
PWM
MIN
0%
PWM DUTY CYCLE
Figure 30. PWM
MIN
Determines Minimum PWM Duty Cycle
It is important to note that more than one PWM output can be
controlled from a single temperature measurement channel. For
example, Remote 1 temperature can control PWM1 and PWM2
outputs. If two different fans are used on PWM1 and PWM2,
then the fan characteristics can be set up differently. So Fan 1
driven by PWM1 can have a different PWM
MIN
value than
that of Fan 2 connected to PWM2. Figure 31 illustrates this as
PWM1
MIN
(front fan) is turned on at a minimum duty cycle of
20%, whereas PWM2
MIN
(rear fan) turns on at a minimum of
40% duty cycle. Note however, that both fans turn on at the
exact same temperature, defined by T
MIN
.
TEMPERATURE
T
MIN
100%
PWM1
MIN
0%
PWM DUTY CYCLE
PWM1
PWM2
PWM2
MIN
Figure 31. Operating Two Different Fans from a
Single-Temperature Channel
Programming the PWM
MIN
Registers
The PWM
MIN
registers are 8-bit registers that allow the minimum
PWM duty cycle for each output to be configured anywhere
from 0% to 100%. This allows minimum PWM duty cycle to be
set in steps of 0.39%.
The value to be programmed into the PWM
MIN
register is
given by
Value decimal
PWM
MIN
(
)
=
0 39
.
Example 1: For a minimum PWM Duty Cycle of 50%,
Value (decimal) = 50/0.39 = 128 decimal
Value = 128 decimal or 80 hex
Example 2: For a minimum PWM duty cycle of 33%,
Value (decimal) = 33/0.39 = 85 decimal
Value = 85 decimal or 54 hex
PWM
MIN
Registers
Reg. 0x64 PWM1 Minimum Duty Cycle = 0x80 (50% default)
Reg. 0x65 PWM2 Minimum Duty Cycle = 0x80 (50% default)
Reg. 0x66 PWM3 Minimum Duty Cycle = 0x80 (50% default)
Fan Speed and PWM Duty Cycle
Note that PWM duty cycle does not directly correlate to fan
speed in rpm. Running a fan at 33% PWM duty cycle does not
equate to running the fan at 33% speed. Driving a fan at 33%
PWM duty cycle actually runs the fan at closer to 50% of its full
speed. This is because fan speed in %rpm relates to the square
root of PWM duty cycle. Given a PWM square wave as the
drive signal, fan speed in RPM equates to
% fan speed
PWM duty cycle
=
10
REV. A
32
ADM1027
Step 5
Determine T
RANGE
for Each Temperature Channel
T
RANGE
is the range of temperature over which automatic fan
control occurs once the programmed T
MIN
temperature has
been exceeded. T
RANGE
is actually a temperature slope and not
an arbitrary value, i.e., a T
RANGE
of 40
C only holds true for
PWM
MIN
= 33%. If PWM
MIN
is increased or decreased, the
effective T
RANGE
is changed, as described later.
TEMPERATURE
T
MIN
100%
PWM
MIN
0%
PWM DUTY CYCLE
T
RANGE
Figure 32. T
RANGE
Parameter Affects Cooling Slope
The T
RANGE
or fan control slope is determined by the following
procedure:
1. Determine the maximum operating temperature for that
channel, e.g., 70
C.
2. Determine experimentally the fan speed (PWM duty cycle
value) will not exceed that temperature at the worst-case
operating points, e.g., 70
C is reached when the fans are
running at 50% PWM duty cycle.
3. Determine the slope of the required control loop to meet
these requirements.
4. Use best fit approximation to determine the most suitable
T
RANGE
value. There is ADM1027 evaluation software avail-
able to calculate the best fit value; ask your local Analog
Devices representative for more details.
T
MIN
100%
33%
0%
PWM DUTY CYCLE
50%
30 C
40 C
Figure 33. Adjusting PWM
MIN
Affects T
RANGE
T
RANGE
is implemented as a slope, which means as PWM
MIN
is
changed, T
RANGE
changes, but the actual slope remains the
same. The higher the PWM
MIN
value, the smaller the effective
T
RANGE
will be, i.e., the fan will reach full speed (100%) at a
lower temperature.
T
MIN
100%
33%
0%
PWM DUTY CYCLE
50%
30 C
40 C
25%
10%
45 C
54 C
Figure 34. Increasing PWM
MIN
Changes Effective T
RANGE
For a given T
RANGE
value, the temperature at which the fan
will run full-speed for different PWM
MIN
values can easily be
calculated:
T
T
MaxD.C.
MinD.C.
T
MAX
MIN
RANGE
=
+
-
(
)
170
where:
T
MAX
= Temperature at which the fan runs full-speed
T
MIN
= Temperature at which the fan will turn on
MaxD.C. = Maximum duty cycle (100%) = 255 decimal
MinD.C. = PWM
MIN
T
RANGE
= PWM duty cycle versus temperature slope
Example: Calculate T
MAX
, given T
MIN
= 30
C, T
RANGE
= 40
C,
and PWM
MIN
= 10% duty cycle = 26 decimal
T
T
MaxD C
MinD C
T
MAX
MIN
RANGE
=
+
-
(
)
. .
. .
170
T
C
C
MAX
= +
-
(
)
30
100
10
40
170
%
%
T
C
C
MAX
= +
-
(
)
30
255
26
40
170
T
MAX
= 84
C (effective T
RANGE
= 54
C)
Example: Calculate T
MAX
, given T
MIN
= 30
C, T
RANGE
= 40
C
and PWM
MIN
= 25% duty cycle = 64 decimal
T
T
MaxD C
MinD C
T
MAX
MIN
RANGE
=
+
-
(
)
. .
. .
170
T
C
C
MAX
= +
-
(
)
30
100
25
40
170
%
%
T
C
C
MAX
= +
-
(
)
30
255
64
40
170
T
MAX
= 75
C (effective T
RANGE
= 45
C)
REV. A
ADM1027
33
Example: Calculate T
MAX
, given T
MIN
= 30
C, T
RANGE
= 40
C,
and PWM
MIN
= 33% duty cycle = 85 decimal
T
T
MaxD C
MinD C
T
MAX
MIN
RANGE
=
+
-
(
)
. .
. .
170
T
C
C
MAX
= +
-
(
)
30
100
33
40
170
%
%
T
C
C
MAX
= +
-
(
)
30
255
85
40
170
T
MAX
= 70
C (effective T
RANGE
= 40
C)
Example: Calculate T
MAX
, given T
MIN
= 30
C, T
RANGE
= 40
C,
and PWM
MIN
= 50% duty cycle = 128 decimal
T
T
MaxD C
MinD C
T
MAX
MIN
RANGE
=
+
-
(
)
. .
. .
170
T
C
C
MAX
= +
-
(
)
30
100
50
40
170
%
%
T
C
C
MAX
= +
-
(
)
30
255
128
40
170
T
MAX
= 60
C (effective T
RANGE
= 30
C)
Selecting a T
RANGE
Slope
The T
RANGE
value can be selected for each temperature channel:
Remote 1, Local and Remote 2 Temp. Bits <7:4> (TRANGE)
of Registers 0x5F to 0x61 define the T
RANGE
value for each
temperature channel.
Bits <7:4>
*
T
RANGE
(
C)
0000
2
0001
2.5
0010
3.33
0011
4
0100
5
0101
6.67
0110
8
0111
10
1000
13.33
1001
16
1010
20
1011
26.67
1100
32 (default)
1101
40
1110
53.33
1111
80
* Register 0x5F configures remote 1 T
RANGE
.
Register 0x60 configures local T
RANGE
.
Register 0x61 configures remote 2 T
RANGE
.
REV. A
34
ADM1027
Step 6
Determine T
THERM
for Each Temperature Channel
T
THERM
is the absolute maximum temperature allowed on a
temperature channel. Above this temperature, a component such
as the CPU or VRM may be operating beyond its safe operating
limit. When the measured temperature exceeds T
THERM
, all fans
are driven at 100% PWM duty cycle (full speed) to provide
critical system cooling. The fans remain running at 100% until
the temperature drops below T
THERM
hysteresis. The hysteresis
value is 4
C.
The T
THERM
limit should be considered the maximum worst-
case operating temperature of the system. Since exceeding any
T
THERM
limit runs all fans at 100%, it has very negative acoustic
effects. Ultimately, this limit should be set up as a fail-safe, and
the user should ensure that it is not exceeded under normal
system operating conditions.
Note that the T
THERM
limits are nonmaskable and affect the fan
speed no matter what automatic fan control settings are config-
ured. This allows some flexibility since a T
RANGE
value can be
selected based on its slope, while a hard limit, e.g., 70
C, can be
programmed as T
MAX
(the temperature at which the fan reaches
full speed) by setting T
THERM
to 70
C.
THERM hysteresis is 4
C.
THERM Registers
Reg. 0x6A Remote 1 THERM Limit = 0x64 (100
C default)
Reg. 0x6B Local Temperature THERM Limit = 0x64
(100
C default)
Reg. 0x6C Remote 2 THERM Limit = 0x64 (100
C default)
T
MIN
PWM DUTY CYCLE
0%
100%
T
THERM
TACHOMETER 1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETERS 3
AND 4
MEASUREMENT
PWM
GENERATOR
PWM
GENERATOR
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM
CONFIG
PWM
MIN
MUX
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
PWM
MIN
PWM
MIN
PWM
CONFIG
PWM
CONFIG
REMOTE 1 =
AMBIENT TEMP
LOCAL =
VRM TEMP
REMOTE 2 =
CPU TEMP
PWM1
TACH1
CPU
FANSINK
FRONT
CHASSIS
REAR
CHASSIS
PWM3
TACH3
PWM2
TACH2
T
RANGE
Figure 35. Understanding How T
THERM
Relates to Automatic Fan Control
REV. A
ADM1027
35
Step 7
Determine T
HYST
for Each Temperature Channel
T
HYST
is the amount of extra cooling a fan provides after the
measured temperature has dropped back below T
MIN
before the
fan turns off. The premise for temperature hysteresis (T
HYST
)
is that without it, the fan would merely chatter, or cycle on and
off regularly, whenever the temperature is hovering about the
T
MIN
setting.
The T
HYST
value chosen will determine the amount of time
needed for the system to cool down or heat up, as the fan is
turning on and off. Values of hysteresis are programmable in
the range 1
C to 15C. Larger values of T
HYST
prevent the fans
chattering on and off as previously described. The T
HYST
default
value is 4
C.
Hysteresis Registers
Reg. 0x6D Remote 1, Local Hysteresis Register
<7:4> = Remote 1 temperature hysteresis (default = 4
C)
<3:0> = Local temperature hysteresis (default = 4
C)
Reg. 0x6E Remote 2 Temperature Hysteresis Register
<7:4> = Remote 2 temperature hysteresis (default = 4
C)
Note that in some applications it is required that the fans not
turn off below T
MIN
, but remain running at PWM
MIN
. Bits <7:5>
of Enhance Acoustics Register 1 (Reg. 0x62) allow the fans to
be turned off or kept spinning below T
MIN
. If the fans are always
on, the T
HYST
value has no effect on the fan when the tempera-
ture drops below T
MIN
.
Enhance Acoustics Register 1 (Reg. 0x62)
Bit 7 (MIN3) = 0, PWM3 is OFF (0% PWM duty cycle) when
temperature is below T
MIN
T
HYST
.
Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle
below T
MIN
T
HYST
.
Bit 6 (MIN2) = 0, PWM2 is OFF (0% PWM duty cycle) when
temperature is below T
MIN
T
HYST
.
Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle
below T
MIN
T
HYST
.
Bit 5 (MIN1) = 0, PWM1 is OFF (0% PWM duty cycle) when
temperature is below T
MIN
T
HYST
.
Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle
below T
MIN
T
HYST
.
PWM DUTY CYCLE
0%
100%
T
RANGE
T
HYST
T
MIN
T
THERM
TACHOMETER 1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETERS 3
AND 4
MEASUREMENT
PWM
GENERATOR
PWM
GENERATOR
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM
CONFIG
PWM
MIN
MUX
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
PWM
MIN
PWM
MIN
PWM
CONFIG
PWM
CONFIG
REMOTE 1 =
AMBIENT TEMP
LOCAL =
VRM TEMP
REMOTE 2 =
CPU TEMP
PWM1
TACH1
CPU
FANSINK
FRONT
CHASSIS
REAR
CHASSIS
PWM3
TACH3
PWM2
TACH2
Figure 36. The T
HYST
Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
REV. A
36
ADM1027
ENHANCING SYSTEM ACOUSTICS
Automatic fan speed control mode reacts instantaneously to
changes in temperature, i.e., the PWM duty cycle will respond
immediately to temperature change. Any impulses in tempera-
ture can cause an impulse in fan noise. For psycho-acoustic
reasons, the ADM1027 can prevent the PWM output from
reacting instantaneously to temperature changes. Enhanced
acoustic mode will control the maximum change in PWM duty
cycle in a given time. The objective is to prevent the fan cycling
up and down and annoying the system user.
Acoustic Enhancement Mode Overview
Figure 37 gives a top-level overview of the automatic fan
control circuitry on the ADM1027 and where acoustic
enhancement fits in. Acoustic enhancement is intended as a
post-design tweak when a system or mechanical engineer is
evaluating best settings for the system. Having determined the
optimal settings for the thermal solution, the engineer can adjust
the system acoustics. The goal is to implement a system that is
acoustically pleasing without causing the user annoyance due to
fan cycling. It is important to realize that although a system may
pass an acoustic noise requirement specification, e.g., 36 dB,
if the fan is annoying, it will fail the consumer test.
The Approach
There are two different approaches to implementing system
acoustic enhancement. The first method is temperature-centric.
This involves smoothing transient temperatures as they are mea-
sured by a temperature source, e.g., Remote 1 temperature.
The temperature values used to calculate PWM duty cycle
values would be smoothed, reducing fan speed variation. However,
this approach causes an inherent delay in updating fan speed
and causes the thermal characteristics of the system to change.
It also causes the system fans to stay on longer than necessary,
since the fan reaction is merely delayed. The user also has no
control over noise from different fans driven by the same tempera-
ture source. Consider controlling a CPU cooler fan (on PWM1)
and a chassis fan (on PWM2) using Remote 1 temperature.
Because the Remote 1 temperature is smoothed, both fans will
be updated at exactly the same rate. If the chassis fan is much
louder than the CPU fan, there is no way to improve its acoustics
without changing the thermal solution of the CPU cooling fan.
The second approach is fan-centric. The idea is to control the
PWM duty cycle driving the fan at a fixed rate, e.g., 6%. Each
time the PWM duty cycle is updated, it is incremented by a
fixed 6%. So the fan ramps smoothly to its newly calculated
speed. If the temperature starts to drop, the PWM duty cycle
immediately decreases by 6% every update. So the fan ramps
smoothly up or down without inherent system delay. Consider
controlling the same CPU cooler fan (on PWM1) and chassis
fan (on PWM2) using Remote 1 temperature. The T
MIN
and
T
RANGE
settings have already been defined in automatic fan
speed control mode, i.e., thermal characterization of the control
loop has been optimized. Now the chassis fan is noisier than the
CPU cooling fan. So PWM2 can be placed into acoustic
enhancement mode independent of PWM1. The acoustics of
the chassis fan can therefore be adjusted without affecting the
acoustic behavior of the CPU cooling fan, even though both
fans are being controlled by Remote 1 temperature. This is
exactly how acoustic enhancement works on the ADM1027.
ACOUSTIC
ENHANCEMENT
TACHOMETER 1
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETERS 3
AND 4
MEASUREMENT
PWM
GENERATOR
PWM
GENERATOR
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM
CONFIG
PWM
MIN
MUX
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
PWM
MIN
PWM
MIN
PWM
CONFIG
PWM
CONFIG
REMOTE 1 =
AMBIENT TEMP
LOCAL =
VRM TEMP
REMOTE 2 =
CPU TEMP
PWM1
TACH1
CPU
FANSINK
FRONT
CHASSIS
REAR
CHASSIS
PWM3
TACH3
PWM2
TACH2
Figure 37. Acoustic Enhancement Smooths Fan Speed Variations Under Automatic Fan Speed Control
REV. A
ADM1027
37
Enabling Acoustic Enhancement for Each PWM Output
ENHANCED ACOUSTICS REGISTER 1 (Reg. 0x62)
<3> = 1 enables acoustic enhancement on PWM1 output.
ENHANCED ACOUSTICS REGISTER 2 (Reg. 0x63)
<7> = 1 enables acoustic enhancement on PWM2 output.
<3> = 1 enables acoustic enhancement on PWM3 output.
Effect of Ramp Rate on Enhanced Acoustics Mode
The PWM signal driving the fan will have a period, T, given by
the PWM drive frequency, f, since T = 1/f. For a given PWM
period, T, the PWM period is subdivided into 255 equal time
slots. One time slot corresponds to the smallest possible incre-
ment in PWM duty cycle. A PWM signal of 33% duty cycle will
thus be high for 1/3 255 time slots and low for 2/3 255
time slots. Therefore, 33% PWM duty cycle corresponds to a
signal that is high for 85 time slots and low for 170 time slots.
170
TIME SLOTS
85
TIME SLOTS
PWM OUTPUT
(ONE PERIOD)
= 255 TIME SLOTS
PWM_OUT
33% DUTY
CYCLE
Figure 38. 33% PWM Duty Cycle Represented in Time Slots
The ramp rates in enhanced acoustics mode are selectable
between 1, 2, 3, 5, 8, 12, 24, and 48. The ramp rates are actu-
ally discrete time slots. For example, if the ramp rate = 8, then
eight time slots will be added to the PWM high duty cycle each
time the PWM duty cycle needs to be increased. If the PWM
duty cycle value needs to be decreased, it will be decreased by
eight time slots. Figure 39 shows how the enhanced acoustics
mode algorithm operates.
READ
TEMPERATURE
CALCULATE
NEW PWM
DUTY CYCLE
IS NEW PWM
VALUE >
PREVIOUS
VALUE?
INCREMENT
PREVIOUS
PWM VALUE
BY RAMP
RATE
YES
NO
DECREMENT
PREVIOUS
PWM VALUE
BY RAMP
RATE
Figure 39. Enhanced Acoustics Algorithm
The enhanced acoustics mode algorithm calculates a new PWM
duty cycle based on the temperature measured. If the new
PWM duty cycle value is greater than the previous PWM value,
then the previous PWM duty cycle value is incremented by
either 1, 2, 3, 5, 8, 12, 24, or 48 time slots (depending on the
settings of the enhanced acoustics registers). If the new PWM
duty cycle value is less than the previous PWM value, then the
previous PWM duty cycle is decremented by 1, 2, 3, 5, 8, 12, 24,
or 48 time slots. Each time the PWM duty cycle is incremented
or decremented, it is stored as the previous PWM duty cycle for
the next comparison.
A ramp rate of 1 corresponds to one time slot, which is 1/255 of
the PWM period. In enhanced acoustics mode, incrementing or
decrementing by 1 changes the PWM output by 1/255 100%.
It is important to note that when using the enhanced acoustics
mode, the fan spin-up should be disabled.
REV. A
38
ADM1027
CHOOSING RAMP RATE FOR ACOUSTIC
ENHANCEMENT
The optimal ramp rate for acoustic enhancement can be found
through system characterization after the thermal optimization
has been finished. Each ramp rate's effects should be logged, if
possible, to determine the best setting for a given solution.
Enhanced Acoustics Register 1 (Reg. 0x62)
<2:0> ACOU Select the ramp rate for PWM1.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
Enhanced Acoustics Register 2 (Reg. 0x63)
<2:0> ACOU3 Select the ramp rate for PWM3.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
<6:4> ACOU2 Select the ramp rate for PWM2.
000 = 1 time slot = 35 sec
001 = 2 time slots = 17.6 sec
010 = 3 time slots = 11.8 sec
011 = 5 time slots = 7 sec
100 = 8 time slots = 4.4 sec
101 = 12 time slots = 3 sec
110 = 24 time slots = 1.6 sec
111 = 48 time slots = 0.8 sec
Another way to view the ramp rates is as the time it takes for the
PWM output to ramp from 0% to 100% duty cycle for an instan-
taneous change in temperature. This can be tested by putting
the ADM1027 into manual mode and changing the PWM output
from 0% to 100% PWM duty cycle. The PWM output takes
35 sec to reach 100% with a ramp rate of 1 time slot selected.
TIME sec
140
0
0.76
120
100
80
60
40
20
0
120
100
80
60
40
20
0
R
TEMP
( C)
POWER DUTY CYCLE (%)
Figure 40. Enhanced Acoustics Mode with Ramp Rate = 48
Figure 40 shows remote temperature plotted against PWM duty
cycle for enhanced acoustics mode. The ramp rate is set to 48,
which corresponds to the fastest ramp rate. Assume that a new
temperature reading is available every 115 ms. With these set-
tings, it took approximately 0.76 seconds to go from 33% duty
cycle to 100% duty cycle (full speed). It can be seen that even
though the temperature increased very rapidly, the fan ramps up
to full speed gradually.
Figure 41 shows how changing the ramp rate from 48 to 8
affects the control loop. The overall response of the fan is
slower. Since the ramp rate is reduced, it takes longer for the
fan to achieve full running speed. In this case, it took approxi-
mately 4.4 sec for the fan to reach full speed.
TIME sec
120
0
4.4
140
120
100
80
60
40
0
100
80
60
40
20
0
20
Figure 41. Enhanced Acoustics Mode with Ramp Rate = 8
As can be seen from the preceding examples, the rate at which
the fan will react to temperature change is dependent on the
ramp rate selected in the enhance acoustics registers. The higher
the ramp rate, the faster the fan will reach the newly calculated
fan speed.
Figure 42 shows the behavior of the PWM output as temperature
varies. As the temperature rises, the fan speed ramps up. Small
drops in temperature will not affect the ramp-up function since
the newly calculated fan speed will still be higher than the previous
PWM value. The enhanced acoustics mode allows the PWM
output to be made less sensitive to temperature variations. This
will be dependent on the ramp rate selected and programmed
into the enhanced acoustics.
90
90
80
70
60
50
40
20
80
70
60
50
40
0
30
10
30
20
10
0
R
TEMP
PWM DUTY CYCLE
Figure 42. How Fan Reacts to Temperature
Variation in Enhanced Acoustics Mode
REV. A
ADM1027
39
OPERATING FROM 3.3 V STANDBY
The ADM1027 has been specifically designed to operate from a
3.3 V STBY supply. In computers that support S3 and S5 states,
the core voltage of the processor will be lowered in these states.
Note that since other voltages can drop or be turned off during
a low power state, these voltage channels will set status bits or
generate
SMBALERTs. It is still necessary to mask out these
channels prior to entering a low power state by using the interrupt
mask registers. When exiting the low power state, the mask bits
can be cleared. This prevents the device from generating unwanted
SMBALERTs during the low power state.
XOR TREE TEST MODE
The ADM1027 includes an XOR tree test mode. This mode is
useful for in-circuit test equipment at board-level testing. By
applying stimulus to the pins included in the XOR tree, it is
possible to detect opens or shorts on the system board. Figure 43
shows the signals that are exercised in the XOR tree test mode.
The XOR tree test is invoked by setting Bit 0 (XEN) of the
XOR tree test enable register (Reg. 0x6F).
PWM1/XTO
PWM3
PWM2
TACH4
TACH3
TACH2
TACH1
VID4
VID3
VID2
VID1
VID0
Figure 43. XOR Tree Test
REV. A
40
ADM1027
Table IV. ADM1027 Registers
Address
R/W
Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable?
0x20
R
2.5 V Reading
9
8
7
6
5
4
3
2
0x00
0x21
R
V
CCP
Reading
9
8
7
6
5
4
3
2
0x00
0x22
R
V
CC
Reading
9
8
7
6
5
4
3
2
0x00
0x23
R
5 V Reading
9
8
7
6
5
4
3
2
0x00
0x24
R
12 V Reading
9
8
7
6
5
4
3
2
0x00
0x25
R
Remote 1 Temperature
9
8
7
6
5
4
3
2
0x80
0x26
R
Local Temperature
9
8
7
6
5
4
3
2
0x80
0x27
R
Remote 2 Temperature
9
8
7
6
5
4
3
2
0x80
0x28
R
TACH1 Low Byte
7
6
5
4
3
2
1
0
0x00
0x29
R
TACH1 High Byte
15
14
13
12
11
10
9
8
0x00
0x2A
R
TACH2 Low Byte
7
6
5
4
3
2
1
0
0x00
0x2B
R
TACH2 High Byte
15
14
13
12
11
10
9
8
0x00
0x2C
R
TACH3 Low Byte
7
6
5
4
3
2
1
0
0x00
0x2D
R
TACH3 High Byte
15
14
13
12
11
10
9
8
0x00
0x2E
R
TACH4 Low Byte
7
6
5
4
3
2
1
0
0x00
0x2F
R
TACH4 High Byte
15
14
13
12
11
10
9
8
0x00
0x30
R/W
PWM1 Current Duty Cycle
7
6
5
4
3
2
1
0
0xFF
0x31
R/W
PWM2 Current Duty Cycle
7
6
5
4
3
2
1
0
0xFF
0x32
R/W
PWM3 Current Duty Cycle
7
6
5
4
3
2
1
0
0xFF
0x3D
R
Device ID Register
7
6
5
4
3
2
1
0
0x27
0x3E
R
Company ID Number
7
6
5
4
3
2
1
0
0x41
0x3F
R
Revision Number
VER
VER
VER
VER
STP
STP
STP
STP
0x60
0x40
R/W
Configuration Register 1
V
CC
TODIS
FSPDIS
V
I
FSPD
RDY
LOCK
STRT
0x00
Yes
0x41
R
Interrupt Status Register 1
OOL
R2T
LT
R1T
5 V
V
CC
V
CCP
2.5 V
0x00
0x42
R
Interrupt Status Register 2
D2
D1
5
FAN3
FAN2
FAN1
OVT
12 V
0x00
0x43
R/W
VID Register
7
6
5
VID4
VID3
VID2
VID1
VID0
0xFF
0x44
R/W
2.5 V Low Limit
7
6
5
4
3
2
1
0
0x00
0x45
R/W
2.5 V High Limit
7
6
5
4
3
2
1
0
0xFF
0x46
R/W
V
CCP
Low Limit
7
6
5
4
3
2
1
0
0x00
0x47
R/W
V
CCP
High Limit
7
6
5
4
3
2
1
0
0xFF
0x48
R/W
V
CC
Low Limit
7
6
5
4
3
2
1
0
0x00
0x49
R/W
V
CC
High Limit
7
6
5
4
3
2
1
0
0xFF
0x4A
R/W
5 V Low Limit
7
6
5
4
3
2
1
0
0x00
0x4B
R/W
5 V High Limit
7
6
5
4
3
2
1
0
0xFF
0x4C
R/W
12 V Low Limit
7
6
5
4
3
2
1
0
0x00
0x4D
R/W
12 V High Limit
7
6
5
4
3
2
1
0
0xFF
0x4E
R/W
Remote 1 Temp Low Limit
7
6
5
4
3
2
1
0
0x81
0x4F
R/W
Remote 1 Temp High Limit
7
6
5
4
3
2
1
0
0x7F
0x50
R/W
Local Temp Low Limit
7
6
5
4
3
2
1
0
0x81
0x51
R/W
Local Temp High Limit
7
6
5
4
3
2
1
0
0x7F
0x52
R/W
Remote 2 Temp Low Limit
7
6
5
4
3
2
1
0
0x81
0x53
R/W
Remote 2 Temp High Limit
7
6
5
4
3
2
1
0
0x7F
0x54
R/W
TACH1 Minimum Low Byte
7
6
5
4
3
2
1
0
0xFF
0x55
R/W
TACH1 Minimum High Byte
15
14
13
12
11
10
9
8
0xFF
0x56
R/W
TACH2 Minimum Low Byte
7
6
5
4
3
2
1
0
0xFF
0x57
R/W
TACH2 Minimum High Byte
15
14
13
12
11
10
9
8
0xFF
0x58
R/W
TACH3 Minimum Low Byte
7
6
5
4
3
2
1
0
0xFF
0x59
R/W
TACH3 Minimum High Byte
15
14
13
12
11
10
9
8
0xFF
0x5A
R/W
TACH4 Minimum Low Byte
7
6
5
4
3
2
1
0
0xFF
0x5B
R/W
TACH4 Minimum High Byte
15
14
13
12
11
10
9
8
0xFF
REV. A
ADM1027
41
Table IV. ADM1027 Registers (continued)
Address
R/W Description
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
Lockable?
0x5C
R/W PWM1 Configuration Register
BHVR
BHVR
BHVR
INV
3
SPIN
SPIN
SPIN
0x62
Yes
0x5D
R/W PWM2 Configuration Register
BHVR
BHVR
BHVR
INV
3
SPIN
SPIN
SPIN
0x62
Yes
0x5E
R/W PWM3 Configuration Register
BHVR
BHVR
BHVR
INV
3
SPIN
SPIN
SPIN
0x62
Yes
0x5F
R/W Remote 1 T
RANGE
/PWM 1 Freq
RANGE RANGE RANGE
RANGE 3
FREQ
FREQ
FREQ
0xC4
Yes
0x60
R/W Local T
RANGE
/PWM 2 Freq
RANGE RANGE RANGE
RANGE 3
FREQ
FREQ
FREQ
0xC4
Yes
0x61
R/W Remote 2 T
RANGE
/PWM 3 Freq
RANGE RANGE RANGE
RANGE 3
FREQ
FREQ
FREQ
0xC4
Yes
0x62
R/W Enhance Acoustics Reg 1
MIN3
MIN2
MIN1
4
EN1
ACOU
ACOU
ACOU
0x00
Yes
0x63
R/W Enhance Acoustics Reg 2
EN2
ACOU2 ACOU2
ACOU2 EN3
ACOU3 ACOU3 ACOU3 0x00
Yes
0x64
R/W PWM1 Min Duty Cycle
7
6
5
4
3
2
1
0
0x80
Yes
0x65
R/W PWM2 Min Duty Cycle
7
6
5
4
3
2
1
0
0x80
Yes
0x66
R/W PWM3 Min Duty Cycle
7
6
5
4
3
2
1
0
0x80
Yes
0x67
R/W Remote 1 Temp T
MIN
7
6
5
4
3
2
1
0
0x5A
Yes
0x68
R/W Local Temp T
MIN
7
6
5
4
3
2
1
0
0x5A
Yes
0x69
R/W Remote 2 Temp T
MIN
7
6
5
4
3
2
1
0
0x5A
Yes
0x6A
R/W Remote 1 THERM Limit
7
6
5
4
3
2
1
0
0x64
Yes
0x6B
R/W Local THERM Limit
7
6
5
4
3
2
1
0
0x64
Yes
0x6C
R/W Remote 2 THERM Limit
7
6
5
4
3
2
1
0
0x64
Yes
0x6D
R/W Remote 1, Local Hysteresis
HYSR1
HYSR1
HYSR1
HYSR1 HYSL
HYSL
HYSL
HYSL
0x44
Yes
0x6E
R/W Remote 2 Temp Hysteresis
HYSR2
HYSR2
HYSR2
HYSR2 RES
RES
RES
RES
0x40
Yes
0x6F
R/W XOR Tree Test Enable
RES
RES
RES
RES
RES
RES
RES
XEN
0x00
Yes
0x70
R/W Remote 1 Temperature Offset
7
6
5
4
3
2
1
0
0x00
Yes
0x71
R/W Local Temperature Offset
7
6
5
4
3
2
1
0
0x00
Yes
0x72
R/W Remote 2 Temperature Offset
7
6
5
4
3
2
1
0
0x00
Yes
0x73
R/W Configuration Register 2
7
CONV
ATTN
AVG
AIN4
AIN3
AIN2
AIN1
0x00
Yes
0x74
R/W Interrupt Mask 1 Register
OOL
R2T
LT
R1T
5 V
V
CC
V
CCP
2.5 V
0x00
0x75
R/W Interrupt Mask 2 Register
D2
D1
5
FAN3
FAN2
FAN1
OVT
12 V
0x00
0x76
R/W Extended Resolution 1
5 V
5 V
V
CC
V
CC
V
CCP
V
CCP
2.5 V
2.5 V
0x00
0x77
R/W Extended Resolution 2
TDM2
TDM2
LTMP
LTMP
TDM1
TDM1
12 V
12 V
0x00
0x78
R/W Configuration Register 3
DC4
DC3
DC2
DC1
FAST
BOOST 1
ALERT 0x00
Yes
0x7B
R/W Fan Pulses per Revolution
FAN4
FAN4
FAN3
FAN3
FAN2
FAN2
FAN1
FAN1
0x55
REV. A
42
ADM1027
Table V. Voltage Reading Registers (Power-On Default = 0x00)
Register Address
R/W
Description
0x20
Read-Only
2.5 V Reading (8 MSBs of reading).
0x21
Read-Only
V
CCP
Reading. Holds processor core voltage measurement (8 MSBs of reading).
0x22
Read-Only
V
CC
Reading. Measures V
CC
through the V
CC
pin (8 MSBs of reading).
0x23
Read-Only
5 V Reading (8 MSBs of reading).
0x24
Read-Only
12 V Reading (8 MSBs of reading).
If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) should be read
first. Once the extended resolution register is read, the associated MSB reading registers are frozen until read. Both the extended
resolution register and the MSB registers are frozen.
Table VI. Temperature Reading Registers (Power-On Default = 0x80)
Register Address
R/W
Description
0x25
Read-Only
Remote 1 Temperature Reading
* (8 MSBs of reading).
0x26
Read-Only
Local Temperature Reading (8 MSBs of reading).
0x27
Read-Only
Remote 2 Temperature Reading
* (8 MSBs of reading).
These temperature readings are in twos complement format.
*Note that a reading of 0x80 in a temperature reading register indicates a diode fault (open or short) on that channel. If the extended resolution bits of these readings
are also being read, the extended resolution registers (Reg. 0x76, 0x77) should be read first. Once the extended resolution register is read, all associated MSB reading
registers are frozen until read. Both the extended resolution register and the MSB registers are frozen.
Table VII. Fan Tachometer Reading Registers (Power-On Default = 0x00)
Register Address
R/W
Description
0x28
Read-Only
TACH1 Low Byte
0x29
Read-Only
TACH1 High Byte
0x2A
Read-Only
TACH2 Low Byte
0x2B
Read-Only
TACH2 High Byte
0x2C
Read-Only
TACH3 Low Byte
0x2D
Read-Only
TACH3 High Byte
0x2E
Read-Only
TACH4 Low Byte
0x2F
Read-Only
TACH4 High Byte
These registers count the number of 11.11
ms periods (based on an internal 90 kHz clock) that occur between a number of consecutive
fan tach pulses (default = 2). The number of tach pulses used to count can be changed using the fan pulses per revolution register
(Reg. 0x7B). This allows the fan speed to be accurately measured. Since a valid fan tachometer reading requires that two bytes are
read; the low byte MUST be read first. Both the low and high bytes are then frozen until read. At power-on, these registers contain
0x0000 until such time as the first valid fan tach measurement is read in to these registers. This prevents false interrupts from occurring
while the fans are spinning up.
A count of 0xFFFF indicates that a fan is:
1. Stalled or Blocked (object jamming the fan)
2. Failed (internal circuitry destroyed)
3. Not Populated (The ADM1027 expects to see a fan connected to
each TACH. If a fan is not connected to that TACH, its TACH
minimum high and low bytes should be set to 0xFFFF.)
4. 2-Wire Instead of 3-Wire Fan
REV. A
ADM1027
43
Table VIII. Current PWM Duty Cycle Registers (Power-On Default = 0xFF)
Register Address
R/W
Description
0x30
Read/Write
PWM1 Current Duty Cycle (0% to 100% duty cycle = 0x00 to 0xFF)
0x31
Read/Write
PWM2 Current Duty Cycle (0% to 100% duty cycle = 0x00 to 0xFF)
0x32
Read/Write
PWM3 Current Duty Cycle (0% to 100% duty cycle = 0x00 to 0xFF)
These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the ADM1027
reports the PWM duty cycles back through these registers. The PWM duty cycle values will vary according to temperature in
automatic fan speed control mode. During fan startup, these registers report back 0x00. In software mode, the PWM duty cycle
outputs can be set to any duty cycle value by writing to these registers.
Table IX. Register 0x40 Configuration Register 1 (Power-On Default = 0x00)
Bit
Name
R/W
Description
<0>
STRT
Read/Write
Logic 1 enables monitoring and PWM control outputs based on the limit settings pro-
grammed. Logic 0 disables monitoring and PWM control based on the default power-up
limit settings. Note that the limit values programmed are preserved even if a LOGIC 0 is
written to this bit and the default settings are enabled. This bit becomes read-only and
cannot be changed once Bit 1 (lock bit) has been written. All limit registers should be
programmed by BIOS before setting this bit to 1 (lockable).
<1>
LOCK
Write Once
Logic 1 locks all limit values to their current settings. Once this bit is set, all lockable
registers become read-only and cannot be modified until the ADM1027 is powered down
and powered up again. This prevents rogue programs such as viruses from modifying
critical system limit settings (lockable).
<2>
RDY
Read-Only
This bit gets set to 1 by the ADM1027 to indicate that the device is fully powered up
and ready to begin systems monitoring.
<3>
FSPD
Read/Write
When set to 1, this runs all fans at full speed. Power-on default = 0. This bit does not get
locked at any time.
<4>
V
I
Read/Write
BIOS should set this bit to 1 when the ADM1027 is configured to measure current
from an ADI ADOPT
VRM controller and measure the CPU's core voltage. This will
allow monitoring software to display CPU watts usage (lockable).
<5>
FSPDIS
Read/Write
Logic 1 disables fan spin-up for two TACH pulses. Instead, the PWM outputs will go
high for the entire fan spin-up timeout selected.
<6>
TODIS
Read/Write
When this bit is set to 1, the SMBus timeout feature is disabled. This allows the ADM1027
to be used with SMBus controllers that cannot handle SMBus timeouts (lockable).
<7>
V
CC
Read/Write
When this bit is set to 1, the ADM1027 rescales its V
CC
pin to measure a 5 V supply.
If this bit is 0, the ADM1027 measures V
CC
as a 3.3 V supply (lockable).
REV. A
44
ADM1027
Table X. Register 0x41 Interrupt Status Register 1 (Power-On Default = 0x00)
Bit
Name
Read/Write
Description
<0>
2.5 V
Read-Only
A 1 indicates the 2.5 V
high or low limit has been exceeded. This bit is cleared on a read
of the status register only if the error condition has subsided.
<1>
V
CCP
Read-Only
A 1 indicates the V
CCP
high or low limit has been exceeded. This bit is cleared on a read
of the status register only if the error condition has subsided.
<2>
V
CC
Read-Only
A 1 indicates the V
CC
high or low limit has been exceeded. This bit is cleared on a read
of the status register only if the error condition has subsided.
<3>
5 V
Read-Only
A 1 indicates the 5 V high or low limit has been exceeded. This bit is cleared on a read of
the status register only if the error condition has subsided.
<4>
R1T
Read-Only
A 1 indicates the Remote 1 low or high temp limit has been exceeded. This bit is
cleared on a read of the status register only if the error condition has subsided.
<5>
LT
Read-Only
A 1 indicates the local low or high temp limit has been exceeded. This bit is cleared on
a read of the status register only if the error condition has subsided.
<6>
R2T
Read-Only
A 1 indicates the Remote 2 low or high temperature limit has been exceeded. This bit is
cleared on a read of the status register only if the error condition has subsided.
<7>
OOL
Read-Only
A 1 indicates that an out-of-limit event has been latched in Status Register 2. This bit is
a logical OR of all status bits in Status Register 2. Software can test this bit in isolation to
determine whether any of the voltage, temperature, or fan speed readings represented by
Status Register 2 are out-of-limit. This saves the need to read Status Register 2 every
interrupt or polling cycle.
Table XI. Register 0x42 Interrupt Status Register 2 (Power-On Default = 0x00)
Bit
Name
Read/Write
Description
<0>
12 V
Read-Only
A 1 indicates the 12 V high or low limit has been exceeded. This bit is cleared on a read
of the status register only if the error condition has subsided.
<1>
OVT
Read-Only
A 1 indicates that one of the THERM overtemperature limits has been exceeded. This bit
is cleared on a read of the status register when the temperature drops below THERM 4
C
<2>
FAN1
Read-Only
A 1 indicates that Fan 1 has dropped below minimum speed or has stalled. This bit is
NOT set when the PWM 1 output is off.
<3>
FAN2
Read-Only
A 1 indicates that Fan 2 has dropped below minimum speed or has stalled. This bit is
NOT set when the PWM 2 output is off.
<4>
FAN3
Read-Only
A 1 indicates that Fan 3 has dropped below minimum speed or has stalled. This bit is
NOT set when the PWM 3 output is off.
<5>
FAN4
Read-Only
A 1 indicates that Fan 4 has dropped below minimum speed or has stalled. This bit is
NOT set when the PWM 3 output is off.
<6>
D1
Read-Only
A 1 indicates either an open or short circuit on the Thermal Diode 1 inputs.
<7>
D2
Read-Only
A 1 indicates either an open or short circuit on the Thermal Diode 2 inputs.
REV. A
ADM1027
45
Table XII. Register 0x43 VID Register (Power-On Default = 0x00 )
Bit
Name
R/W
Description
<4:0>
VID[4:0]
Read-Only
The VID[4:0] inputs from the CPU to indicate the expected processor core voltage. On
power-up, these bits reflect the state of the VID pins, even if monitoring is not enabled.
<7:5>
Reserved
Read-Only
Reserved for future use.
Table XIII. Voltage Limit Registers
Register Address
R/W
Description
Power-On Default
0x44
Read/Write
2.5 V Low Limit
0x00
0x45
Read/Write
2.5 V High Limit
0xFF
0x46
Read/Write
V
CCP
Low Limit
0x00
0x47
Read/Write
V
CCP
High Limit
0xFF
0x48
Read/Write
V
CC
Low Limit
0x00
0x49
Read/Write
V
CC
High Limit
0xFF
0x4A
Read/Write
5 V Low Limit
0x00
0x4B
Read/Write
5 V High Limit
0xFF
0x4C
Read/Write
12 V Low Limit
0x00
0x4D
Read/Write
12 V High Limit
0xFF
Setting the Configuration Register 1 lock bit has no effect on these registers.
High Limits: An interrupt is generated when a value exceeds its high limit ( > comparison).
Low Limits: An interrupt is generated when a value is equal to or below its low limit (
comparison).
Table XIV. Temperature Limit Registers
Register Address
R/W
Description
Power-On Default
0x4E
Read/Write
Remote 1 Temperature Low Limit
0x81
0x4F
Read/Write
Remote 1 Temperature High Limit
0x7F
0x50
Read/Write
Local Temperature Low Limit
0x81
0x51
Read/Write
Local Temperature High Limit
0x7F
0x52
Read/Write
Remote 2 Temperature Low Limit
0x81
0x53
Read/Write
Remote 2 Temperature High Limit
0x7F
Exceeding any of these temperature limits by 1
o
C will cause the appropriate status bit to be set in the interrupt status register. Setting
the Configuration Register 1 lock bit has no effect on these registers.
High Limits: An interrupt is generated when a value exceeds its high limit ( > comparison).
Low Limits: An interrupt is generated when a value is equal to or below its low limit (
comparison).
REV. A
46
ADM1027
Table XV. Fan Tachometer Limit Registers
Register Address
R/W
Description
Power-On Default
0x54
Read/Write
TACH 1 Minimum Low Byte
0xFF
0x55
Read/Write
TACH 1 Minimum High Byte
0xFF
0x56
Read/Write
TACH 2 Minimum Low Byte
0xFF
0x57
Read/Write
TACH 2 Minimum High Byte
0xFF
0x58
Read/Write
TACH 3 Minimum Low Byte
0xFF
0x59
Read/Write
TACH 3 Minimum High Byte
0xFF
0x5A
Read/Write
TACH 4 Minimum Low Byte
0xFF
0x5B
Read/Write
TACH 4 Minimum High Byte
0xFF
Exceeding any of the TACH limit registers by 1 indicates that the fan is running too slowly or has stalled. The appropriate status bit
will be set in Interrupt Status Register 2 to indicate the fan failure. Setting the Configuration Register 1 lock bit has no effect on
these registers.
Table XVI. PWM Configuration Registers
Register Address
R/W
Description
Power-On Default
0x5C
Read/Write
PWM1 Configuration
0x62
0x5D
Read/Write
PWM2 Configuration
0x62
0x5E
Read/Write
PWM3 Configuration
0x62
Bit
Name
Read/Write
Description
<2:0>
SPIN
Read/Write
These bits control the startup timeout for PWMx. The PWM output stays high until two
(Fan Startup
valid TACH rising edges are seen from the fan. If there is not a valid TACH signal during
Timeout)
the fan TACH measurement directly after the fan startup timeout period, then the TACH
measurement will read 0xFFFF and Status Register 2 will reflect the fan fault. If the
TACH minimum high and low byte contains 0xFFFF or 0x0000, then the Status Register
2 bit will not be set, even if the fan has not started.
000 = No startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
101 = 1 sec
110 = 2 sec
111 = 4 sec
Note: Do not program 100.
<3>
Reserved
Read-Only
Reserved for future use.
<4>
INV
Read/Write
This bit inverts the PWM output. The default is 0, which corresponds to a logic high
output for 100% duty cycle. Setting this bit to 1, inverts the PWM output, so 100% duty
cycle corresponds to a logic low output.
<7:5>
BHVR
Read/Write
These bits assign each fan to a particular temperature sensor for localized cooling.
000 = Remote 1 temperature controls PWMx (automatic fan control mode).
001 = Local temperature controls PWMx (automatic fan control mode).
010 = Remote 2 temperature controls PWMx (automatic fan control mode).
011 = PWMx runs full speed (default).
100 = PWMx disabled.
101 = Fastest speed calculated by local and Remote 2 temperature controls PWMx.
110 = Fastest speed calculated by all three temperatures controls PWMx.
111 = Manual mode. PWM duty cycle registers (Reg. 0x30 to 0x32) become writable.
These registers become read-only when the configuration register 1 lock bit is set to 1. Any subsequent attempts to write to these
registers will fail.
REV. A
ADM1027
47
Table XVII. TEMP T
RANGE
/PWM Frequency Registers
Register Address
R/W
Description
Power-On Default
0x5F
Read/Write
Remote 1 T
RANGE
/PWM 1 Frequency
0xC4
0x60
Read/Write
Local Temperature T
RANGE
/PWM 2 Frequency
0xC4
0x61
Read/Write
Remote 2 T
RANGE
/PWM 3 Frequency
0xC4
Bit
Name
Read/Write
Description
<2:0>
FREQ
Read/Write
These bits control the PWMx frequency.
000 = 11.0 Hz
001 = 14.7 Hz
010 = 22.1 Hz
011 = 29.4 Hz
100 = 35.3 Hz (default)
101 = 44.1 Hz
110 = 58.8 Hz
111 = 88.2 Hz
<3>
Reserved
Read/Write
Reserved for future use.
<7:4>
RANGE
Read/Write
These bits determine the PWM duty cycle versus temperature slope for automatic
fan control.
0000 = 2
o
C
0001 = 2.5
o
C
0010 = 3.33
o
C
0011 = 4
o
C
0100 = 5
o
C
0101 = 6.67
o
C
0110 = 8
o
C
0111 = 10
o
C
1000 = 13.33
o
C
1001 = 16
o
C
1010 = 20
o
C
1011 = 26.67
o
C
1100 = 32
o
C (default)
1101 = 40
o
C
1110 = 53.33
o
C
1111 = 80
o
C
These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers
will have no effect.
REV. A
48
ADM1027
Table XVIII. Register 0x62 Enhance Acoustics Register 1 (Power-On Default = 0x00)
Bit
Name
R/W
Description
<2:0>
ACOU
Read-Only
These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jump-
ing instantaneously to its newly calculated speed, PWM1 will ramp gracefully at the rate
determined by these bits. This feature enhances the acoustics of the fan being driven by
the PWM1 output.
Time slot increase
Time for 33% to 100%
000 = 1
35 sec
001 = 2
17.6 sec
010 = 3
1.8 sec
011 = 5
7 sec
100 = 8
4.4 sec
101 = 12
3 sec
110 = 24
1.6 sec
111 = 48
0.8 sec
<3>
EN1
Read/Write
When this bit is 1, acoustic enhancement is enabled on PWM1 output. When
acoustic enhancement is enabled, fan spin-up time should be disabled.
<4>
Reserved
Read-Only
Reserved for future use.
<5>
MIN1
Read/Write
When the ADM1027 is in automatic fan control mode, this bit defines whether PWM 1
is off (0% duty cycle) or at PWM 1 minimum duty cycle when the controlling temperature
is below its T
MIN
hysteresis value.
0 = 0% duty cycle below T
MIN
hysteresis
1 = PWM 1 minimum duty cycle below T
MIN
hysteresis
<6>
MIN2
Read/Write
When the ADM1027 is in automatic fan speed control mode, this bit defines whether
PWM 2 is off (0% duty cycle) or at PWM 2 minimum duty cycle when the controlling
temperature is below its T
MIN
hysteresis value.
0 = 0% duty cycle below T
MIN
hysteresis
1 = PWM 2 minimum duty cycle below T
MIN
hysteresis
<7>
MIN3
Read/Write
When the ADM1027 is in automatic fan speed control mode, this bit defines whether
PWM 3 is off (0% duty cycle) or at PWM 3 minimum duty cycle when the controlling
temperature is below its T
MIN
hysteresis value.
0 = 0% duty cycle below T
MIN
hysteresis
1 = PWM 3 minimum duty cycle below T
MIN
hysteresis
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
REV. A
ADM1027
49
Table XIX. Register 0x63 Enhance Acoustics Register 2 (Power-On Default = 0x00)
Bit
Name
R/W
Description
<2:0>
ACOU3
Read/Write
These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping
instantaneously to its newly calculated speed, PWM3 will ramp gracefully at the rate
determined by these bits. This effect enhances the acoustics of the fan being driven by the
PWM3 output.
Time slot increase
Time for 33% to 100%
000 = 1
35 sec
001 = 2
17.6 sec
010 = 3
11.8 sec
011 = 5
7 sec
100 = 8
4.4 sec
101 = 12
3 sec
110 = 24
1.6 sec
111 = 48
0.8 sec
<3>
EN3
Read/Write
When this bit is 1, acoustic enhancement is enabled on PWM3 output. When acoustic
enhancement is enabled, fan spin-up time should be disabled.
<6:4>
ACOU2
Read/Write
These bits select the ramp rate applied to the PWM2 output. Instead of PWM2 jumping
instantaneously to its newly calculated speed, PWM2 will ramp gracefully at the rate
determined by these bits. This effect enhances the acoustics of the fans being driven by
the PWM2 output.
Time slot increase
Time for 33% to 100%
000 = 1
35 sec
001 = 2
17.6 sec
010 = 3
11.8 sec
011 = 5
7 sec
100 = 8
4.4 sec
101 = 12
3 sec
110 = 24
1.6 sec
111 = 48
0.8 sec
<7>
EN2
Read/Write
When this bit is 1, acoustic enhancement is enabled on PWM2 output. When acoustic
enhancement is enabled, fan spin-up time should be disabled.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
REV. A
50
ADM1027
Table XX. PWM Minimum Duty Cycle Registers
Register Address
R/W
Description
Power-On Default
0x64
Read/Write
PWM1 Minimum Duty Cycle
0x80 (50% duty cycle)
0x65
Read/Write
PWM2 Minimum Duty Cycle
0x80 (50% duty cycle)
0x66
Read/Write
PWM3 Minimum Duty Cycle
0x80 (50% duty cycle)
Bit
Name
Read/Write
Description
<7:0>
PWM Duty
Read/Write
These bits define the PWM
MIN
duty cycle for the PWMx output.
0x00 = 0% duty cycle (fan off)
0x40 = 25% duty cycle
0x80 = 50% duty cycle
0xFF = 100% duty cycle (fan full speed)
These registers become read-only when the ADM1027 is in automatic fan control mode.
Table XXI. T
MIN
Registers
Register Address
R/W
Description
Power-On Default
0x67
Read/Write
Remote 1 Temperature T
MIN
0x5A (90
o
C)
0x68
Read/Write
Local Temperature T
MIN
0x5A (90
o
C)
0x69
Read/Write
Remote 2 Temperature T
MIN
0x5A (90
o
C)
These are the T
MIN
registers for each temperature channel. When the temperature measured exceeds T
MIN
, the appropriate fan will
run at minimum speed and increase with temperature according to T
RANGE
.
These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers
will have no effect.
Table XXII. Therm Limit Registers
Register Address
R/W
Description
Power-On Default
0x6A
Read/Write
Remote 1 THERM Limit
0x64 (100
o
C)
0x6B
Read/Write
Local THERM Limit
0x64 (100
o
C)
0x6C
Read/Write
Remote 2 THERM Limit
0x64 (100
o
C)
If any temperature measured exceeds its THERM limit, all PWM outputs will drive their fans at 100% duty cycle. This is a fail-safe
mechanism incorporated to cool the system in the event of a critical overtemperature. It also ensures some level of cooling in the
event that software or hardware locks up. If set to 0x80, this feature is disabled. The PWM output will remain at 100% until the
temperature drops below THERM limit 4
C .
These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers
will have no effect.
Table XXIII. Temperature Hysteresis Registers
Register Address
R/W
Description
Power-On Default
0x6D
Read/Write
Remote 1, Local Temperature Hysteresis
0x44
0x6E
Read/Write
Remote 2 Temperature Hysteresis
0x40
Each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for
that channel falls below its T
MIN
value, the fan will remain running at PWM
MIN
duty cycle until the temperature = T
MIN
hysteresis.
Up to 15
o
C of hysteresis may be assigned to any temperature channel. Setting the hysteresis value lower than 4
o
C will cause the fan
to switch on and off regularly when the temperature is close to T
MIN
.
These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers
will have no effect.
REV. A
ADM1027
51
Table XXIV. XOR Tree Test Enable
Register Address
R/W
Description
Power-On Default
0x6F
Read/Write
XOR Tree Test Enable Register
0x00
<0>
XEN
If the XEN bit is set to 1, the device enters the XOR tree test mode. Clearing the bit
removes the device from the XOR tree test mode.
<7:1>
Reserved
Unused. Do not write to these bits.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXV. Remote 1 Temperature Offset
Register Address
R/W
Description
Power-On Default
0x70
Read/Write
Remote 1 Temperature Offset
0x00
<7:0>
Read/Write
Allows a twos complement offset value to be automatically added to or subtracted from
the Remote 1 temperature reading. This is to compensate for any inherent system offsets
such as PCB trace resistance. LSB value = 1
o
C.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXVI. Local Temperature Offset
Register Address
R/W
Description
Power-On Default
0x71
Read/Write
Local Temperature Offset
0x00
<7:0>
Read/Write
Allows a twos complement offset value to be automatically added to or subtracted from
the local temperature reading. LSB value = 1
o
C.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXVII. Remote 2 Temperature Offset
Register Address
R/W
Description
Power-On Default
0x72
Read/Write
Remote 2 Temperature Offset
0x00
<7:0>
Read/Write
Allows a twos complement offset value to be automatically added to or subtracted from
the Remote 2 temperature reading. This is to compensate for any inherent system off-
sets such as PCB trace resistance. LSB value = 1
o
C.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
REV. A
52
ADM1027
Table XXVIII. Register 0x73 Configuration Register 2 (Power-On Default = 0x00)
Bit
Name
R/W
Description
0
AIN1
Read/Write
AIN1 = 0, speed of 3-wire fans measured using the TACH output from the fan.
AIN1 = 1, Pin 11 is reconfigured to measure the speed of 2-wire fans using an external
sensing resistor and coupling capacitor.
1
AIN2
Read/Write
AIN2 = 0, speed of 3-wire fans measured using the TACH output from the fan.
AIN2 = 1, Pin 12 is reconfigured to measure the speed of 2-wire fans using an external
sensing resistor and coupling capacitor.
2
AIN3
Read/Write
AIN3 = 0, speed of 3-wire fans measured using the TACH output from the fan.
AIN3 = 1, Pin 9 is reconfigured to measure the speed of 2-wire fans using an external
sensing resistor and coupling capacitor.
3
AIN4
Read/Write
AIN4 = 0, speed of 3-wire fans measured using the TACH output from the fan.
AIN4 = 1, Pin 14 is reconfigured to measure the speed of 2-wire fans using an external
sensing resistor and coupling capacitor.
4
AVG
Read/Write
AVG = 1, averaging on the temperature and voltage measurements is turned off. This
allows measurements on each channel to be made much faster.
5
ATTN
Read/Write
ATTN = 1, the ADM1027 removes the attenuators from the 2.5 V, V
CCP
, 5 V, and
12 V inputs. The inputs can be used for other functions such as connecting up external
sensors.
6
CONV
Read/Write
CONV = 1, the ADM1027 is put into a single-channel ADC conversion mode.
In this mode, the ADM1027 can be made to read continuously from one input only,
e.g., Remote 1 temperature. It is also possible to start ADC conversions using an
external clock on Pin 11 by setting Bit 2 of Test Register 2 (Reg. 0x7F). This mode
could be useful if, for example, the user wanted to characterize/profile CPU temperature
quickly. The appropriate ADC channel is selected by writing to Bits <7:5> of TACH1
minimum high byte register (0x55).
Bits <7:5> Reg. 0x55
Channel Selected
`
000
2.5 V
001
V
CCP
010
V
CC
(3.3 V)
011
5 V
100
12 V
101
Remote 1 Temp
110
Local Temp
111
Remote 2 Temp
7
Reserved
Read/Write
Reserved for future use
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
REV. A
ADM1027
53
Table XXIX. Register 0x74 Interrupt Mask Register 1 (Power-On Default <7:0> = 0x00)
Bit
Name
R/W
Description
0
2.5 V
Read/Write
A 1 masks
SMBALERT for out-of-limit conditions on the 2.5 V channel.
1
V
CCP
Read/Write
A 1 masks
SMBALERT for out-of-limit conditions on the V
CCP
channel.
2
V
CC
Read/Write
A 1 masks
SMBALERT for out-of-limit conditions on the V
CC
channel.
3
5 V
Read/Write
A 1 masks
SMBALERT for out-of-limit conditions on the 5 V channel.
4
R1T
Read/Write
A 1 masks
SMBALERT for out-of-limit conditions on the Remote 1 temperature channel.
5
LT
Read/Write
A 1 masks
SMBALERT for out-of-limit conditions on the local temperature channel.
6
R2T
Read/Write
A 1 masks
SMBALERT for out-of-limit conditions on the Remote 2 temperature channel.
7
OOL
Read/Write
This bit needs to be set to 1 to allow masking in the Interrupt Mask Register 2. If this bit
is not set to 1, then setting a bit in Mask Register 2 will have no effect.
Table XXX. Register 0x75 Interrupt Mask Register 2 (Power-On Default <7:0> = 0x00)
Bit
Name
R/W
Description
0
12 V
Read/Write
A 1 masks
SMBALERT for out-of-limit conditions on the 12 V channel.
1
OVT
Read-Only
A 1 masks
SMBALERT for overtemperature THERM conditions.
2
FAN1
Read/Write
A 1 masks
SMBALERT for a Fan 1 fault.
3
FAN2
Read/Write
A 1 masks
SMBALERT for a Fan 2 fault.
4
FAN3
Read/Write
A 1 masks
SMBALERT for a Fan 3 fault.
5
FAN4
Read/Write
A 1 masks
SMBALERT for a Fan 4 fault.
6
D1
Read/Write
A 1 masks
SMBALERT for a diode open or short on Remote 1 channel.
7
D2
Read/Write
A 1 masks
SMBALERT for a diode open or short on Remote 2 channel.
Table XXXI. Register 0x76 Extended Resolution Register 1
Bit
Name
R/W
Description
<1:0>
2.5 V
Read-Only
2.5 V LSBs. Holds the 2 LSBs of the 10-bit 2.5 V measurement.
<3:2>
V
CCP
Read-Only
V
CCP
LSBs. Holds the 2 LSBs of the 10-bit V
CCP
measurement.
<5:4>
V
CC
Read-Only
V
CC
LSBs. Holds the 2 LSBs of the 10-bit V
CC
measurement.
<7:6>
5 V
Read-Only
5 V LSBs. Holds the 2 LSBs of the 10-bit 5 V measurement.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
Table XXXII. Register 0x77 Extended Resolution Register 2
Bit
Name
R/W
Description
<1:0>
12 V
Read-Only
12 V LSBs. Holds the 2 LSBs of the 10-bit 12 V measurement.
<3:2>
TDM1
Read-Only
Remote 1 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 1 temperature
measurement.
<5:4>
LTMP
Read-Only
Local temperature LSBs. Holds the 2 LSBs of the 10-bit local temperature measurement.
<7:6>
TDM2
Read-Only
Remote 2 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 2 temperature
measurement.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
REV. A
54
ADM1027
Table XXXIII. Register 0x78 Configuration Register 3 (Power-On Default = 0x00)
Bit
Name
R/W
Description
<0>
ALERT
Read/Write
ALERT = 1, Pin 10 (PWM2/
SMBALERT) is configured as an SMBALERT interrupt
output to indicate out-of-limit error conditions. Default = 0 = PWM2.
<1>
Reserved
Read/Write
Reserved for future use.
<2>
Reserved
Read/Write
Reserved for future use.
<3>
FAST
Read/Write
FAST = 1 enables fast TACH measurements on all channels. This increases the
TACH measurement rate from once per second, to once per 250 ms (4 ).
<4>
DC1
Read/Write
DC1 = 1 enables TACH measurements to be continuously made on TACH1.
<5>
DC2
Read/Write
DC2 = 2 enables TACH measurements to be continuously made on TACH2.
<6>
DC3
Read/Write
DC3 = 1 enables TACH measurements to be continuously made on TACH3.
<7>
DC4
Read/Write
DC4 = 1 enables TACH measurements to be continuously made on TACH4.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXXIV. Register 0x7B Fan Pulses Per Revolution Register (Power On Default = 0x55)
Bit
Name
R/W
Description
<1:0>
FAN1
Read/Write
Sets number of pulses to be counted when measuring FAN1 speed. Can be used to
determine fan's pulses per revolution number for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
<3:2>
FAN2
Read/Write
Sets number of pulses to be counted when measuring FAN2 speed. Can be used to
determine fan's pulses per revolution number for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
<5:4>
FAN3
Read/Write
Sets number of pulses to be counted when measuring FAN3 speed. Can be used to
determine fan's pulses per revolution for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
<7:6>
FAN4
Read/Write
Sets number of pulses to be counted when measuring FAN4 speed. Can be used to
determine fan's pulses per revolution for unknown fan type.
Pulses Counted
00 = 1
01 = 2 (default)
10 = 3
11 = 4
REV. A
ADM1027
55
Table XXXV. Register 0x7E Manufacturer's Test Register 1 (Power-On Default = 0x00)
Bit
Name
Read/Write
Description
<7:0>
Reserved
Read-Only
Manufacturer's Test Register. These bits are reserved for the manufacturer's test
purposes and should NOT be written to under normal operation.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
Table XXXVI. Register 0x7F Manufacturer's Test Register 2 (Power-On Default = 0x00)
Bit
Name
Read/Write
Description
<7:0>
Reserved
Read-Only
Manufacturer's Test Register. These bits are reserved for the manufacturer's test
purposes and should NOT be written to under normal operation.
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register
will have no effect.
REV. A
C0292803/03(A)
56
ADM1027
Revision History
Location
Page
3/03--Data Sheet changed from REV. 0 to REV. A.
Changes to Nulling Out Temperature Errors section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Changes to Tables XXVXXVII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
OUTLINE DIMENSIONS
24-Lead Shrink Small Outline Package [QSOP]
(RQ-24)
Dimensions shown in millimeters and (inches)
24
13
12
1
0.236
BSC
PIN 1
0.154
BSC
SEATING
PLANE
0.010
0.004
0.012
0.008
0.025
BSC
0.069
0.053
0.010
0.006
0.050
0.016
8
0
0.065
0.049
COPLANARITY
0.004
0.341
BSC
COMPLIANT TO JEDEC STANDARDS MO-137AE
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