PWM Fan Speed Controller with FanSense Technology
2002 Microchip Technology Inc.
DS21444C-page 1
M
TC642
Features
Temperature Proportional Fan Speed for Acoustic
Control and Longer Fan Life
Efficient PWM Fan Drive
3.0V to 5.5V Supply Range:
- Fan Voltage Independent of TC642
Supply Voltage
- Supports any Fan Voltage
FanSenseTM
Fault Detection Circuits Protect
Against Fan Failure and Aid System Testing
Shutdown Mode for "Green" Systems
Supports Low Cost NTC/PTC Thermistors
Space Saving 8-Pin MSOP Package
Over-temperature Indication
Applications
Power Supplies
Personal Computers
File Servers
Telecom Equipment
UPSs, Power Amps, etc.
General Purpose Fan Speed Control
Available Tools
Fan Controller Demonstration Board (TC642DEMO)
Fan Controller Evaluation Kit (TC642EV)
Package Types
General Description
The TC642 is a switch mode fan speed controller for
use with brushless DC fans. Temperature proportional
speed control is accomplished using pulse width mod-
ulation (PWM). A thermistor (or other voltage output
temperature sensor) connected to the V
IN
input fur-
nishes the required control voltage of 1.25V to 2.65V
(typical) for 0% to 100% PWM duty cycle. Minimum fan
speed is set by a simple resistor divider on the V
MIN
input. An integrated Start-up Timer ensures reliable
motor start-up at turn-on, coming out of shutdown
mode or following a transient fault. A logic low applied
to V
MIN
(Pin 3) causes fan shutdown.
The TC642 also features Microchip Technology's pro-
prietary FanSenseTM technology for increasing system
reliability. In normal fan operation, a pulse train is
present at SENSE (Pin 5). A missing pulse detector
monitors this pin during fan operation. A stalled, open
or unconnected fan causes the TC642 to trigger its
Start-up Timer once. If the fault persists, the FAULT
output goes low and the device is latched in its shut-
down mode. FAULT is also asserted if the PWM
reaches 100% duty cycle, indicating a possible thermal
runaway situation, although the fan continues to run.
See Section 5.0, "Typical Applications", for more
information and system design guidelines.
The TC642 is available in the standard 8-pin plastic
DIP, SOIC and MSOP packages and is available in the
commercial, extended commercial and industrial
temperature ranges.
1
8
2
7
3
6
4
5
TC642
GND
CF
V
IN
V
MIN
FAULT
SENSE
V
DD
V
OUT
SOIC/PDIP/MSOP
PWM Fan Speed Controller with FanSense
TM
Technology
TC642
DS21444C-page 2
2002 Microchip Technology Inc.
Functional Block Diagram
FAULT
SHDN
SENSE
OTF
GND
70mV (typ.)
10k
V
MIN
V
IN
C
F
V
DD
V
OUT
TC642
Control
Logic
+
V
OTF
V
SHDN
+
+
+
+
3 x TPWM
Timer
Start-up
Timer
Clock
Generator
Missing
Pulse
Detect
2002 Microchip Technology Inc.
DS21444C-page 3
TC642
1.0
ELECTRICAL
CHARACTERISTICS
Absolute Maximum Ratings*
Supply Voltage ......................................................... 6V
Input Voltage, Any Pin.... (GND 0.3V) to (V
DD
+0.3V)
Package Thermal Resistance:
PDIP (R
JA
)............................................. 125C/W
SOIC (R
JA
) ............................................155C/W
MSOP (R
JA
) .......................................... 200C/W
Specified Temperature Range ........... -40C to +125C
Storage Temperature Range.............. -65C to +150C
*Stresses above those listed under "Absolute Maximum Rat-
ings" may cause permanent damage to the device. These are
stress ratings only and functional operation of the device at
these or any other conditions above those indicated in the
operation sections of the specifications is not implied. Expo-
sure to absolute maximum rating conditions for extended peri-
ods may affect device reliability.
ELECTRICAL SPECIFICATIONS
Note 1: Ensured by Design, not tested.
Electrical Characteristics: T
MIN
< T
A
< T
MAX
, V
DD
= 3.0V to 5.5V, unless otherwise specified.
Symbol
Parameter
Min
Typ
Max
Units
Test Conditions
V
DD
Supply Voltage
3.0
--
5.5
V
I
DD
Supply Current, Operating
--
0.5
1.0
mA
Pins 6, 7 Open,
C
F
= 1 F, V
IN
= V
C(MAX)
I
DD(SHDN)
Supply Current, Shutdown Mode
--
25
--
A
Pins 6, 7 Open,
C
F
= 1 F, V
MIN
= 0.35V,
Note 1
I
IN
V
IN
,
V
MIN
Input Leakage
- 1.0
--
+1.0
A
Note 1
V
OUT
Output
t
R
V
OUT
Rise Time
--
--
50
sec
I
OH
= 5 mA, Note 1
t
F
V
OUT
Fall Time
--
--
50
sec
I
OL
= 1 mA, Note 1
t
SHDN
Pulse Width (On V
MIN
) to
Clear Fault Mode
30
--
--
sec
V
SHDN
, V
HYST
Specifications,
Note 1
I
OL
Sink Current at V
OUT
Output
1.0
--
--
mA
V
OL
= 10% of V
DD
I
OH
Source Current at V
OUT
Output
5.0
--
--
mA
V
OH
= 80% of V
DD
V
IN
, V
MIN
Inputs
V
C(MAX),
V
OTF
Input Voltage at V
IN
or V
MIN
for 100% PWM Duty Cycle
2.5
2.65
2.8
V
V
C(SPAN)
V
C(MAX)
- V
C(MIN)
1.3
1.4
1.5
V
V
SHDN
Voltage Applied to V
MIN
to
ensure Shutdown Mode
--
--
V
DD
x 0.13
V
V
REL
Voltage Applied to V
MIN
to
Release Shutdown Mode
V
DD
x 0.19
--
--
V
V
DD
= 5V
Pulse Width Modulator
F
PWM
PWM Frequency
26
30
34
Hz
C
F
= 1.0 F
SENSE Input
V
TH(SENSE)
SENSE Input Threshold
Voltage with Respect to GND
50
70
90
mV
Note 1
FAULT Output
V
OL
Output Low Voltage
--
--
0.3
V
I
OL
= 2.5 mA
t
MP
Missing Pulse Detector Timer
--
32/F
--
Sec
t
STARTUP
Start-up Timer
--
32/F
--
Sec
t
DIAG
Diagnostic Timer
--
3/F
--
Sec
TC642
DS21444C-page 4
2002 Microchip Technology Inc.
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
PIN FUNCTION TABLE
2.1
Analog Input (V
IN
)
The thermistor network (or other temperature sensor)
connects to the V
IN
input. A voltage range of 1.25V to
2.65V (typical) on this pin drives an active duty cycle of
0% to 100% on the V
OUT
pin.
2.2
Analog Output (C
F
)
C
F
is the positive terminal for the PWM ramp generator
timing capacitor. The recommended C
F
is 1 F for
30 Hz PWM operation.
2.3
Analog Input (V
MIN
)
An external resistor divider connected to the V
MIN
input
sets the minimum fan speed by fixing the minimum
PWM duty cycle (1.25V to 2.65V = 0% to 100%, typi-
cal). The TC642 enters shutdown mode when V
MIN
V
SHDN
. During shutdown, the FAULT output is inactive
and supply current falls to 25 A (typical). The TC642
exits shutdown mode when V
MIN
V
REL
(see
Section 5.0, "Typical Applications").
2.4
Ground (GND)
GND denotes the ground terminal.
2.5
Analog Input (SENSE)
Pulses are detected at the SENSE pin as fan rotation
chops the current through a sense resistor. The
absence of pulses indicates a fault.
2.6
Digital Output (FAULT)
The FAULT line goes low to indicate a fault condition.
When FAULT goes low due to a fan fault condition, the
device is latched in shutdown mode until deliberately
cleared or until power is cycled. FAULT may be con-
nected to V
MIN
if a hard shutdown is desired. FAULT
will also be asserted when the PWM reaches 100%
duty cycle, indicating that maximum cooling capability
has been reached and a possible over-temperature
condition may occur. This is a non-latching state and
the FAULT output will go high when the PWM duty
cycle goes below 100%.
2.7
Digital Output (V
OUT
)
V
OUT
is an active high complimentary output that drives
the base of an external NPN transistor (via an appropri-
ate base resistor) or the gate of an N-channel MOS-
FET. This output has asymmetrical drive (see
Section 1.0, "Electrical Characteristics").
2.8
Power Supply Input (V
DD
)
V
DD
may be independent of the fan's power supply
(see Section 1.0, "Electrical Characteristics").
Pin No.
Symbol
Description
1
V
IN
Analog Input
2
C
F
Analog Output
3
V
MIN
Analog Input
4
GND
Ground Terminal
5
SENSE
Analog Input
6
FAULT
Digital (Open Collector) Output
7
V
OUT
Digital Output
8
V
DD
Power Supply Input
2002 Microchip Technology Inc.
DS21444C-page 5
TC642
3.0
DETAILED DESCRIPTION
3.1
PWM
The PWM circuit consists of a ramp generator and
threshold detector. The frequency of the PWM is deter-
mined by the value of the capacitor connected to the C
F
input. A frequency of 30 Hz is recommended
(C
F
= 1 F). The PWM is also the time base for the
Start-up Timer (see Section 3.4, "Start-Up Timer"). The
PWM voltage control range is 1.25V to 2.65V (typical)
for 0% to 100% output duty cycle.
3.2
FAULT Output
The TC642 detects faults in two ways.
First, pulses appearing at SENSE due to the PWM
turning on are blanked, with the remaining pulses
filtered by a missing pulse detector. If consecutive
pulses are not detected for 32 PWM cycles (
1 Sec if
C
F
= 1 F), the Diagnostic Timer is activated, and V
OUT
is driven high continuously for three PWM cycles
(
100 msec if C
F
= 1 F). If a pulse is not detected
within this window, the Start-up Timer is triggered (see
Section 3.4). This should clear a transient fault condi-
tion. If the missing pulse detector times out again, the
PWM is stopped and FAULT goes low. When FAULT is
activated due to this condition, the device is latched in
shutdown mode and will remain off indefinitely.
The TC642 may be configured to continuously attempt
fan restarts, if so desired.
Continuous restart mode is enabled by connecting the
FAULT output to V
MIN
through a 0.01 F capacitor, as
shown in Figure 3-1. When connected in this manner,
the TC642 automatically attempts to restart the fan
every time a fault condition occurs. When the FAULT
output is driven low, the V
MIN
input is momentarily
pulled below V
SHDN
, initiating a reset and clearing the
fault condition. Normal fan start-up is then attempted as
previously described. The FAULT output may be
connected to external logic (or the interrupt input of a
microcontroller) to shut the TC642 down if multiple fault
pulses are detected at approximately one second
intervals. Diode D
1
, capacitor C
1
and resistors R
5
and
R
6
are provided to ensure fan restarts are the result of
a fan fault and not an over-temperature fault. A CMOS
logic OR gate may be substituted for these
components, if available.
FIGURE 3-1:
Fan Fault Output Circuit.
Note:
At this point, action must be taken to restart
the fan by momentarily pulling V
MIN
below
V
SHDN
, or cycling system power. In either
case, the fan cannot remain disabled due
to a fault condition, as severe system dam-
age could result. If the fan cannot be
restarted, the system should be shut down.
FAULT
SENSE
R
3
R
1
R
5
10k
D
1
R
4
GND
From
System
Shutdown
Controller
(Optional)
*The parallel combination of R
3
and R
4
must be >10 k
.
Q
1
+12V
+5V
V
DD
V
IN
V
MIN
V
OUT
R
BASE
R
6
1k
V
DD
R
SENSE
C
SENSE
C
F
1
F
C
F
TC642
Fan
C
B
0.01
F
1
8
6
7
5
4
2
3
From
Temp
Sensor
+5V
0.01
F
1
0
TC642
RESET
Fault
Detected
C
1
Q
2
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