REV. B
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
AD7816/AD7817/AD7818
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
Analog Devices, Inc., 2000
Single- and 4-Channel, 9 s, 10-Bit ADCs
with On-Chip Temperature Sensor
FUNCTIONAL BLOCK DIAGRAM
FEATURES
10-Bit ADC with 9 s Conversion Time
One (AD7818) and Four (AD7817) Single-Ended Analog
Input Channels
The AD7816 Is a Temperature Measurement Only Device
On-Chip Temperature Sensor
Resolution of 0.25 C
2 C Error from 40 C to +85 C
55 C to +125 C Operating Range
Wide Operating Supply Range
2.7 V to 5.5 V
Inherent Track-and-Hold Functionality
On-Chip Reference (2.5 V 1%)
Over-Temperature Indicator
Automatic Power-Down at the End of a Conversion
Low Power Operation
4 W at a Throughput Rate of 10 SPS
40 W at a Throughput Rate of 1 kSPS
400 W at a Throughput Rate of 10 kSPS
Flexible Serial Interface
APPLICATIONS
Ambient Temperature Monitoring (AD7816)
Thermostat and Fan Control
High Speed Microprocessor
Temperature Measurement and Control
Data Acquisition Systems with Ambient Temperature
Monitoring (AD7817 and AD7818)
Industrial Process Control
Automotive
Battery Charging Applications
GENERAL DESCRIPTION
The AD7818 and AD7817 are 10-bit, single- and 4-channel
A/D converters with on-chip temperature sensor that can oper-
ate from a single 2.7 V to 5.5 V power supply. Each part con-
tains a 9
s successive-approximation converter based around
a capacitor DAC, an on-chip temperature sensor with an accu-
racy of
2C, an on-chip clock oscillator, inherent track-and-
hold functionality and an on-chip reference (2.5 V). The
AD7816 is a temperature monitoring only device in a SOIC/
SOIC package.
The on-chip temperature sensor of the AD7817 and AD7818
can be accessed via Channel 0. When Channel 0 is selected and
a conversion is initiated, the resulting ADC code at the end of
the conversion gives a measurement of the ambient temperature
with a resolution of
0.25C. See Measuring Temperature section
of the data sheet.
The AD7816, AD7817, and AD7818 have a flexible serial
interface that allows easy interfacing to most microcontrollers.
The interface is compatible with the Intel 8051, Motorola
SPITM and QSPITM protocols and National Semiconductors
MICROWIRETM protocol. For more information refer to the
Serial Interface section of this data sheet.
The AD7817 is available in a narrow body 0.15" 16-lead Small
Outline IC (SOIC), in a 16-lead, Thin Shrink Small Outline
Package (TSSOP), while the AD7816/AD7818 come in an
8-lead Small Outline IC (SOIC) and an 8-lead microsmall
Outline IC (
SOIC).
PRODUCT HIGHLIGHTS
1. The devices have an on-chip temperature sensor that allows an
accurate measurement of the ambient temperature to be
made. The measurable temperature range is 55
C to +125C.
2. An over-temperature indicator is implemented by carrying
out a digital comparison of the ADC code for Channel 0
(temperature sensor) with the contents of the on-chip over-
temperature register. The over-temperature indicator pin goes
logic low when a predetermined temperature is exceeded.
3. The automatic power-down feature enables the AD7816,
AD7817, and AD7818 to achieve superior power perfor-
mance at slower throughput rates, e.g., 40
W at 1 kSPS
throughput rate.
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
CHARGE
REDISTRIBUTION
DAC
CLOCK
D
OUT
SCLK
RD/
WR
CONVST
AGND
CONTROL
REG
A
B
OVER-TEMP
REG
A > B
OTI
CONTROL
LOGIC
V
BALANCE
SAMPLING
CAPACITOR
MUX
REF
2.5V
TEMP
SENSOR
REF
IN
V
DD
DATA
OUT
D
IN
DGND
BUSY
CS
V
IN1
V
IN2
V
IN3
V
IN4
AD7817
2
REV. B
AD7816/AD7817/AD7818
Parameter
A Version
*B Version
*S Version
Unit
Test Conditions/Comments
DYNAMIC PERFORMANCE
Sample Rate = 100 kSPS, Any
Channel, f
IN
= 20 kHz
Signal to (Noise + Distortion) Ratio
2
58
58
58
dB min
Total Harmonic Distortion
2
65
65
65
dB max
75 dB typ
Peak Harmonic or Spurious Noise
2
65
65
65
dB max
75 dB typ
Intermodulation Distortion
2
fa =19.9 kHz, fb = 20.1 kHz
Second Order Terms
67
67
67
dB typ
Third Order Terms
67
67
67
dB typ
Channel-to-Channel Isolation
2
80
80
80
dB typ
f
IN
= 20 kHz
DC ACCURACY
Any Channel
Resolution
10
10
10
Bits
Minimum Resolution for Which
No Missing Codes are Guaranteed
10
10
10
Bits
Relative Accuracy
2
1
1
1
LSB max
Differential Nonlinearity
2
1
1
1
LSB max
Gain Error
2
2
2
2
LSB max
External Reference
10
10
+20/10
LSB max
Internal Reference
Gain Error Match
2
1/2
1/2
1/2
LSB max
Offset Error
2
2
2
2
LSB max
Offset Error Match
1/2
1/2
1/2
LSB max
TEMPERATURE SENSOR
1
Measurement Error
External Reference V
REF
= 2.5 V
Ambient Temperature 25
C
2
1
2
C max
T
MIN
to T
MAX
3
2
3
C max
Measurement Error
On-Chip Reference
Ambient Temperature 25
C
2.25
2.25
2.25
C max
T
MIN
to T
MAX
3
3
6
C max
Temperature Resolution
1/4
1/4
1/4
C/LSB
REFERENCE INPUT
3, 4
REF
IN
Input Voltage Range
3
2.625
2.625
2.625
V max
2.5 V + 5%
2.375
2.375
2.375
V min
2.5 V 5%
Input Impedance
40
40
40
k
min
Input Capacitance
10
10
10
pF max
ON-CHIP REFERENCE
5
Nominal 2.5 V
Temperature Coefficient
3
80
80
150
ppm/
C typ
CONVERSION RATE
Track/Hold Acquisition Time
4
400
400
400
ns max
Source Impedance < 10
Conversion Time
Temperature Sensor
27
27
27
s max
Channels 1 to 4
9
9
9
s max
POWER REQUIREMENTS
V
DD
5.5
5.5
5.5
V max
For Specified Performance
2.7
2.7
2.7
V min
I
DD
Logic Inputs = 0 V or V
DD
Normal Operation
2
2
2
mA max
1.6 mA typ
Using External Reference
1.75
1.75
1.75
mA max
2.5 V External Reference Connected
Power-Down (V
DD
= 5 V)
10
10
12.5
A max
5.5
A typ
Power-Down (V
DD
= 3 V)
4
4
4.5
A max
2
A typ
Auto Power-Down Mode
V
DD
= 3 V
10 SPS Throughput Rate
6.4
6.4
6.4
W typ
See Power vs. Throughput Section
1 kSPS Throughput Rate
48.8
48.8
48.8
W typ
for Description of Power Dissipa-
10 kSPS Throughput Rate
434
434
434
W typ
tion in Auto Power-Down Mode
Power-Down
12
12
13.5
W max
Typically 6
W
AD7817SPECIFICATIONS
1
(V
DD
= 2.7 V to 5.5 V, GND = 0 V, REF
IN
= 2.5 V unless otherwise noted)
3
REV. B
AD7816/AD7818
6
SPECIFICATIONS
1
(V
DD
= 2.7 V to 5.5 V, GND = 0 V, REF
IN
= 2.5 V unless
otherwise noted)
Parameter
A Version
Unit
Test Conditions/Comments
DYNAMIC PERFORMANCE (AD7818 Only)
Sample Rate = 100 kSPS, Any Channel,
f
IN
= 20 kHz
Signal to (Noise + Distortion) Ratio
2
57
dB min
Total Harmonic Distortion
2
65
dB max
75 dB typ
Peak Harmonic or Spurious Noise
2
67
dB typ
75 dB typ
Intermodulation Distortion
2
fa = 19.9 kHz, fb = 20.1 kHz
Second Order Terms
67
dB typ
Third Order Terms
67
dB typ
Channel-to-Channel Isolation
2
80
dB typ
f
IN
= 20 kHz
DC ACCURACY (AD7818 Only)
Any Channel
Resolution
10
Bits
Minimum Resolution for Which
No Missing Codes are Guaranteed
10
Bits
Relative Accuracy
2
1
LSB max
Differential Nonlinearity
2
1
LSB max
Gain Error
2
10
LSB max
Offset Error
2
4
LSB max
TEMPERATURE SENSOR
1
Measurement Error
External Reference V
REF
= 2.5 V
Ambient Temperature 25
C
2
C max
T
MIN
to T
MAX
3
C max
Measurement Error
On-Chip Reference
Ambient Temperature 25
C
2
C max
T
MIN
to T
MAX
3
C max
Temperature Resolution
1/4
C/LSB
REFERENCE INPUT
3, 4
(AD7816 Only)
REF
IN
Input Voltage Range
3
2.625
V max
2.5 V + 5%
2.375
V min
2.5 V 5%
Input Impedance
50
k
min
Input Capacitance
10
pF max
ON-CHIP REFERENCE
5
Nominal 2.5 V
Temperature Coefficient
3
30
ppm/
C typ
CONVERSION RATE
Track/Hold Acquisition Time
4
400
ns max
Source Impedance < 10
Conversion Time
Temperature Sensor
27
s max
Channel 1
9
s max
(AD7818 Only)
POWER REQUIREMENTS
V
DD
5.5
V max
For Specified Performance
2.7
V min
I
DD
Logic Inputs = 0 V or V
DD
Normal Operation
2
mA max
1.3 mA typ
Using External Reference
1.75
mA max
2.5 V External Reference Connected
Power-Down (V
DD
= 5 V)
10.75
A max
6
A typ
Power-Down (V
DD
= 3 V)
4.5
A max
2
A typ
Auto Power-Down Mode
V
DD
= 3 V
10 SPS Throughput Rate
6.4
W typ
See Power vs. Throughput Section for
1 kSPS Throughput Rate
48.8
W typ
Description of Power Dissipation in
10 kSPS Throughput Rate
434
W typ
Auto Power-Down Mode
Power-Down
13.5
W max
Typically 6
W
AD7816/AD7817/AD7818
4
Parameter
A Version
*B Version
*S Version
Unit
Test Conditions/Comments
ANALOG INPUTS
7
(AD7817 and AD7818)
Input Voltage Range
V
REF
V
REF
V
REF
V max
0
0
0
V min
Input Leakage
1
1
1
A min
Input Capacitance
10
10
10
pF max
LOGIC INPUTS
4
Input High Voltage, V
INH
2.4
2.4
2.4
V min
V
DD
= 5 V
10%
Input Low Voltage, V
INL
0.8
0.8
0.8
V max
V
DD
= 5 V
10%
Input High Voltage, V
INH
2
2
2
V min
V
DD
= 3 V
10%
Input Low Voltage, V
INL
0.4
0.4
0.4
V max
V
DD
= 3 V
10%
Input Current, I
IN
3
3
3
A max
Typically 10 nA, V
IN
= 0 V to V
DD
Input Capacitance, C
IN
10
10
10
pF max
LOGIC OUTPUTS
4
Output High Voltage, V
OH
I
SOURCE
= 200
A
4
4
4
V min
V
DD
= 5 V
10%
2.4
2.4
2.4
V min
V
DD
= 3 V
10%
Output Low Voltage, V
OL
I
SINK
= 200
A
0.4
0.4
0.4
V max
V
DD
= 5 V
10%
0.2
0.2
0.2
V max
V
DD
= 3 V
10%
High Impedance Leakage Current
1
1
1
A max
High Impedance Capacitance
15
15
15
pF max
NOTES
*B and S Versions apply to AD7817 only. For operating temperature ranges, see Ordering Guide.
1
AD7816 and AD7817 temperature sensors specified with external 2.5 V reference, AD7818 specified with on-chip reference. All other specifications with external
and on-chip reference (2.5 V). For V
DD
= 2.7 V, T
A
= 85
C max and temperature sensor measurement error = 3C.
2
See Terminology.
3
The accuracy of the temperature sensor is affected by reference tolerance. The relationship between the two is explained in the section titled Temperature Measure-
ment Error Due to Reference Error.
4
Sample tested during initial release and after any redesign or process change that may affect this parameter.
5
On-chip reference shuts down when external reference is applied.
6
All specifications are typical for AD7818 at temperatures above 85
C and with V
DD
greater than 3.6 V.
7
Refers to the input current when the part is not converting. Primarily due to reverse leakage current in the ESD protection diodes.
Specifications subject to change without notice.
CHARGE
REDISTRIBUTION
DAC
CLOCK
DATA
OUT
D
IN/OUT
SCLK
RD/
WR
CONVST
AGND
CONTROL
REG
A
B
OVER-TEMP
REG
A > B
OTI
CONTROL
LOGIC
V
BALANCE
SAMPLING
CAPACITOR
MUX
REF
2.5V
TEMP
SENSOR
REF
IN
V
DD
AD7816
Figure 1. AD7816 Functional Block Diagram
CHARGE
REDISTRIBUTION
DAC
CLOCK
GENERATOR
DATA
OUT
D
IN/OUT
SCLK
RD/
WR
CONVST
AGND
CONTROL
REG
A
B
OVER-TEMP
REG
A > B
OTI
CONTROL
LOGIC
V
BALANCE
SAMPLING
CAPACITOR
MUX
REF
2.5V
TEMP
SENSOR
V
DD
V
IN1
AD7818
Figure 2. AD7818 Functional Block Diagram
AD7816/AD7817/AD7818SPECIFICATIONS
1
REV. B
AD7816/AD7817/AD7818
5
REV. B
TIMING CHARACTERISTICS
1, 2
Parameter
A, B Versions
Unit
Test Conditions/Comments
t
POWER-UP
2
s max
Power-Up Time from Rising Edge of
CONVST
t
1a
9
s max
Conversion Time Channels 1 to 4
t
1b
27
s max
Conversion Time Temperature Sensor
t
2
20
ns min
CONVST Pulsewidth
t
3
50
ns max
CONVST Falling Edge to BUSY Rising Edge
t
4
0
ns min
CS Falling Edge to RD/WR Falling Edge Setup Time
t
5
0
ns min
RD/
WR Falling Edge to SCLK Falling Edge Setup
t
6
10
ns min
D
IN
Setup Time before SCLK Rising Edge
t
7
10
ns min
D
IN
Hold Time after SCLK Rising Edge
t
8
40
ns min
SCLK Low Pulsewidth
t
9
40
ns min
SCLK High Pulsewidth
t
10
0
ns min
CS Falling Edge to RD/WR Rising Edge Setup Time
t
11
0
ns min
RD/
WR Rising Edge to SCLK Falling Edge Setup Time
t
12
3
20
ns max
D
OUT
Access Time after RD/
WR Rising Edge
t
13
3
20
ns max
D
OUT
Access Time after SCLK Falling Edge
t
14a
3, 4
30
ns max
D
OUT
Bus Relinquish Time after Falling Edge of RD/
WR
t
14b
3, 4
30
ns max
D
OUT
Bus Relinquish Time after Rising Edge of
CS
t
15
150
ns max
BUSY Falling Edge to OTI Falling Edge
t
16
40
ns min
RD/
WR Rising Edge to OTI Rising Edge
t
17
400
ns min
SCLK Rising Edge to
CONVST Falling Edge (Acquisition Time of T/H)
NOTES
1
Sample tested during initial release and after any redesign or process change that may affect this parameter. All input signals are measured with tr = tf = 1 ns (10% to
90% of 5 V) and timed from a voltage level of 1.6 V.
2
See Figures 16, 17, 20 and 21.
3
These figures are measured with the load circuit of Figure 3. They are defined as the time required for D
OUT
to cross 0.8 V or 2.4 V for V
DD
= 5 V
10% and 0.4 V
or 2 V for V
DD
= 3 V
10%, as quoted on the specifications page of this data sheet.
4
These times are derived from the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 3. The measured number is then
extrapolated back to remove the effects of charging or discharging the 50 pF capacitor. This means that the times quoted in the timing characteristics are the true bus
relinquish times of the part and as such are independent of external bus loading capacitances.
Specifications subject to change without notice.
1.6V
I
OL
200 A
200 A
I
OL
TO
OUTPUT
PIN
C
L
50pF
Figure 3. Load Circuit for Access Time and Bus Relinquish Time
(V
DD
= 2.7 V to 5.5 V, GND = 0 V, REF
IN
= 2.5 V. All specifications T
MIN
to T
MAX
unless
otherwise noted)
AD7816/AD7817/AD7818
6
REV. B
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 AD7816/AD7817/AD7818 feature proprietary ESD protection circuitry, perma-
nent 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.
ABSOLUTE MAXIMUM RATINGS
1
(
T
A
= 25
C unless otherwise noted)
V
DD
to AGND . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 V to +7 V
V
DD
to DGND . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 V to +7 V
Analog Input Voltage to AGND
V
IN1
to V
IN4
. . . . . . . . . . . . . . . . . . . 0.3 V to V
DD
+ 0.3 V
Reference Input Voltage to AGND
2
. . . 0.3 V to V
DD
+ 0.3 V
Digital Input Voltage to DGND . . . . . . 0.3 V to V
DD
+ 0.3 V
Digital Output Voltage to DGND . . . . . 0.3 V to V
DD
+ 0.3 V
Storage Temperature Range . . . . . . . . . . . . 65
C to +150C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150
C
TSSOP, Power Dissipation . . . . . . . . . . . . . . . . . . . . 450 mW
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 120
C/W
Lead Temperature, Soldering . . . . . . . . . . . . . . . . . . 260
C
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215
C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220
C
16-Lead SOIC Package, Power Dissipation . . . . . . . . 450 mW
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 100
C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215
C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220
C
8-Lead SOIC Package, Power Dissipation . . . . . . . . . 450 mW
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 157
C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215
C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220
C
ORDERING GUIDE
Temperature
Temperature
Package
Branding
Package
Model
Range
Error @ +25
C
Description
Information
Options
AD7816AR
55
C to +125C
2C
8-Lead Narrow Body (SOIC)
SO-8
AD7816ARM
55
C to +125C
2C
8-Lead
SOIC
C4A
RM-8
AD7817AR
40
C to +85C
2C
16-Lead Narrow Body (SOIC)
R-16A
AD7817BR
40
C to +85C
1C
16-Lead Narrow Body (SOIC)
R-16A
AD7817ARU
40
C to +85C
2C
16-Lead (TSSOP)
RU-16
AD7817BRU
40
C to +85C
1C
16-Lead (TSSOP)
RU-16
AD7817SR
55
C to +125C
2C
16-Lead Narrow Body (SOIC)
R-16A
AD7818AR
55
C to +125C
2C
8-Lead Narrow Body (SOIC)
SO-8
AD7818ARM
55
C to +125C
2C
8-Lead
SOIC
C3A
RM-8
SOIC Package, Power Dissipation . . . . . . . . . . . . . . 450 mW
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 206
C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . 215
C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220
C
NOTES
1
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 listed in the operational sections
of this specification is not implied. Exposure to absolute maximum rating condi-
tions for extended periods may affect device reliability.
2
If the Reference Input Voltage is likely to exceed V
DD
by more than 0.3 V (e.g.,
during power-up) and the reference is capable of supplying 30 mA or more, it is
recommended to use a clamping diode between the REF
IN
pin and V
DD
pin. The
diagram below shows how the diode should be connected.
REF
IN
V
DD
BAT81
AD7816/AD7817
WARNING!
ESD SENSITIVE DEVICE
AD7816/AD7817/AD7818
7
REV. B
AD7817 PIN FUNCTION DESCRIPTIONS
Pin
Mnemonic
Description
1
CONVST
Logic Input Signal. The convert start signal. A 10-bit analog-to-digital conversion is initiated on the
falling edge of this signal. The falling edge of this signal places the track/hold in hold mode. The track/
hold goes into track mode again at the end of the conversion. The state of the
CONVST signal is checked
at the end of a conversion. If it is logic low, the AD7817 will power-down--see Operating Mode section
of the data sheet.
2
BUSY
Logic Output. The busy signal is logic high during a temperature or voltage A/D conversion. The signal
can be used to interrupt a microcontroller when a conversion has finished.
3
OTI
Logic Output. The Over-Temperature Indicator (
OTI) is set logic low if the result of a conversion on
Channel 0 (Temperature Sensor) is greater that an eight bit word in the Over-Temperature Register
(OTR). The signal is reset at the end of a serial read operation, i.e., a rising RD/
WR edge when CS is low.
4
CS
Logic Input Signal. The chip select signal is used to enable the serial port of the AD7817. This is neces-
sary if the AD7817 is sharing the serial bus with more than one device.
5
AGND
Analog Ground. Ground reference for track/hold, comparator and capacitor DAC.
6
REF
IN
Analog Input. An external 2.5 V reference can be connected to the AD7817 at this pin. To enable the on-
chip reference the REF
IN
pin should be tied to AGND. If an external reference is connected to the
AD7817, the internal reference will shut down.
710
V
IN1
to V
IN4
Analog Input Channels. The AD7817 has four analog input channels. The input channels are single-
ended with respect to AGND (analog ground). The input channels can convert voltage signals in the
range 0 V to V
REF
. A channel is selected by writing to the Address Register of the AD7817--see Control
Byte section.
11
V
DD
Positive Supply Voltage, 2.7 V to 5.5 V.
12
DGND
Digital Ground. Ground reference for digital circuitry.
13
D
OUT
Logic Output With a High Impedance State. Data is clocked out of the AD7817 serial port at this pin.
This output goes into a high impedance state on the falling edge of RD/
WR or on the rising edge of the
CS signal, whichever occurs first.
14
D
IN
Logic Input. Data is clocked into the AD7817 at this pin.
15
SCLK
Clock Input For the Serial Port. The serial clock is used to clock data into and out of the AD7817. Data
is clocked out on the falling edge and clocked in on the rising edge.
16
RD/
WR
Logic Input Signal. The read/write signal is used to indicate to the AD7817 whether the data transfer
operation is a read or a write. The RD/
WR should be set logic high for a read operation and logic low for
a write operation.
PIN CONFIGURATION
SOIC/TSSOP
14
13
12
11
16
15
10
9
8
1
2
3
4
7
6
5
TOP VIEW
(Not to Scale)
AD7817
CONVST
D
OUT
D
IN
SCLK
RD/
WR
BUSY
O T I
CS
V
IN4
V
DD
DGND
AGND
REF
IN
V
IN1
V
IN2
V
IN3
AD7816/AD7817/AD7818
8
REV. B
AD7816 AND AD7818 PIN FUNCTION DESCRIPTIONS
Pin
Mnemonic
Description
1
CONVST
Logic Input Signal. The convert start signal initiates a 10-bit analog-to-digital conversion on the
falling edge of the this signal. The falling edge of this signal places the track/hold in hold mode.
The track/hold goes into track mode again at the end of the conversion. The state of the
CONVST signal is checked at the end of a conversion. If it is logic low, the AD7816 and
AD7818 will power down--see Operating Mode section of the data sheet.
2
OTI
Logic Output. The Over-Temperature Indicator (
OTI) is set logic low if the result of a conver-
sion on Channel 0 (Temperature Sensor) is greater that an 8-bit word in the Over-Tem-
perature Register (OTR). The signal is reset at the end of a serial read operation, i.e., a rising
RD/
WR edge.
3
GND
Analog and Digital Ground.
4 (AD7818)
V
IN
Analog Input Channel. The input channel is single-ended with respect to GND. The input
channel can convert voltage signals in the range 0 V to 2.5 V. The input channel is selected by
writing to the Address Register of the AD7818--see Control Byte section.
4 (AD7816)
REF
IN
Reference Input. An external 2.5 V reference can be connected to the AD7816 at this pin. To
enable the on-chip reference the REF
IN
pin should be tied to AGND. If an external reference is
connected to the AD7816, the internal reference will shut down.
5
V
DD
Positive supply voltage, 2.7 V to 5.5 V.
6
D
IN/OUT
Logic Input and Output. Serial data is clocked in and out of the AD7816/AD7818 at this pin.
7
SCLK
Clock Input For the Serial Port. The serial clock is used to clock data into and out of the
AD7816/AD7818. Data is clocked out on the falling edge and clocked in on the rising edge.
8
RD/
WR
Logic Input. The read/write signal is used to indicate to the AD7816 and AD7818 whether
the next data transfer operation is a read or a write. The RD/
WR should be set logic high for a
read operation and logic low for a write.
PIN CONFIGURATIONS
SOIC/ SOIC (AD7816)
1
2
3
4
8
7
6
5
TOP VIEW
(Not to Scale)
AD7816
CONVST
D
IN/OUT
SCLK
RD/
WR
V
DD
GND
REF
IN
OTI
SOIC/ SOIC (AD7818)
1
2
3
4
8
7
6
5
TOP VIEW
(Not to Scale)
AD7818
CONVST
D
IN/OUT
SCLK
RD/
WR
V
DD
GND
V
IN
OTI
TERMINOLOGY
Signal to (Noise + Distortion) Ratio
This is the measured ratio of signal to (Noise + Distortion) at
the output of the A/D converter. The signal is the rms amplitude
of the fundamental. Noise is the rms sum of all nonfundamen-
tal signals up to half the sampling frequency (f
S
/2), excluding dc.
The ratio is dependent upon the number of quantization levels
in the digitization process; the more levels, the smaller the
quantization noise. The theoretical Signal to (Noise + Distortion)
Ratio for an ideal N-bit converter with a sine wave input is
given by:
Signal to (Noise + Distortion) = (6.02 N + 1.76) dB
Thus for a 10-bit converter, this is 62 dB.
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the rms sum of
harmonics to the fundamental. For the AD7891 it is defined as:
THD (dB)
= 20 log
V
2
2
+V
3
2
+V
4
2
+V
5
2
+V
6
2
V
1
where V
1
is the rms amplitude of the fundamental and V
2
, V
3
,
V
4
, V
5
and V
6
are the rms amplitudes of the second through the
sixth harmonics.
Peak Harmonic or Spurious Noise
Peak harmonic or spurious noise is defined as the ratio of the
rms value of the next largest component in the ADC output
spectrum (up to f
S
/2 and excluding dc) to the rms value of the
fundamental. Normally, the value of this specification is deter-
mined by the largest harmonic in the spectrum, but for parts
where the harmonics are buried in the noise floor, it will be a
noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities will create distortion
products at sum and difference frequencies of mfa
nfb where
m, n = 0, 1, 2, 3, etc. Intermodulation terms are those for which
neither m nor n are equal to zero. For example, the second
order terms include (fa + fb) and (fa fb), while the third order
terms include (2fa + fb), (2fa fb), (fa + 2fb) and (fa 2fb).
AD7816/AD7817/AD7818
9
REV. B
CONTROL BYTE
The AD7816, AD7817, and AD7818 contain two on-chip regis-
ters, the Address Register and the Over-Temperature Register.
These registers can be accessed by carrying out an 8-bit serial
write operation to the devices. The 8-bit word or control byte
written to the AD7816, AD7817, and AD7818 is transferred to
one of the two on-chip registers as follows.
The AD7816, AD7817, and AD7818 are tested using the CCIF
standard where two input frequencies near the top end of the
input bandwidth are used. In this case, the second and third
order terms are of different significance. The second order terms
are usually distanced in frequency from the original sine waves
while the third order terms are usually at a frequency close to
the input frequencies. As a result, the second and third order
terms are specified separately. The calculation of the intermodu-
lation distortion is as per the THD specification where it is the
ratio of the rms sum of the individual distortion products to the
rms amplitude of the fundamental expressed in dBs.
Channel-to-Channel Isolation
Channel-to-channel isolation is a measure of the level of
crosstalk between channels. It is measured by applying a full-
scale 20 kHz sine wave signal to one input channel and deter-
mining how much that signal is attenuated in each of the other
channels. The figure given is the worst case across all four
channels.
Relative Accuracy
Relative accuracy or endpoint nonlinearity is the maximum
deviation from a straight line passing through the endpoints of
the ADC transfer function.
Differential Nonlinearity
This is the difference between the measured and the ideal
1 LSB change between any two adjacent codes in the ADC.
Offset Error
This is the deviation of the first code transition (0000 . . . 000)
to (0000 . . . 001) from the ideal, i.e., AGND + 1 LSB.
Offset Error Match
This is the difference in Offset Error between any two channels.
Gain Error
This is the deviation of the last code transition (1111 . . . 110) to
(1111 . . . 111) from the ideal, i.e., VREF 1 LSB, after the
offset error has been adjusted out.
Gain Error Match
This is the difference in Gain Error between any two channels.
Track/Hold Acquisition Time
Track/hold acquisition time is the time required for the output
of the track/hold amplifier to reach its final value, within
1/2 LSB, after the end of conversion (the point at which the
track/hold returns to track mode). It also applies to situations
where a change in the selected input channel takes place or
where there is a step input change on the input voltage applied
to the selected V
IN
input of the AD7817 or AD7818. It means
that the user must wait for the duration of the track/hold acqui-
sition time after the end of conversion or after a channel change/
step input change to V
IN
before starting another conversion, to
ensure that the part operates to specification.
Address Register
If the five MSBs of the control byte are logic zero, the three
LSBs of the control byte are transferred to the Address Regis-
ter--see Figure 4. The Address Register is a 3-bit-wide register
used to select the analog input channel on which to carry out a
conversion. It is also used to select the temperature sensor,
which has the address 000. Table I shows the selection. The
Internal Reference selection connects the input of the ADC to a
band gap reference. When this selection is made and a conver-
sion is initiated, the ADC output should be approximately mid-
scale. After power-up the default channel selection is DB2 = DB1
= DB0 = 0 (Temperature Sensor).
Table I. Channel Selection
DB2
DB1
DB0 Channel Selection
Device
0
0
0
Temperature Sensor
All
0
0
1
Channel 1
AD7817/AD7818
0
1
0
Channel 2
AD7817
0
1
1
Channel 3
AD7817
1
0
0
Channel 4
AD7817
1
1
1
Internal Ref (1.23 V)
All
Over-Temperature Register
If any of the five MSBs of the control byte are logic one then the
entire eight bits of the control byte are transferred to the Over-
Temperature Register--see Figure 4. At the end of a tempera-
ture conversion a digital comparison is carried out between the
8 MSBs of the temperature conversion result (10 bits) and the
contents of the Over-Temperature Register (8 bits). If the result
of the temperature conversion is greater that the contents of the
Over-Temperature Register (OTR), then the Over-Temperature
Indicator (
OTI) goes logic low. The resolution of the OTR is
1
C. The lowest temperature that can be written to the OTR is
95
C and the highest is +152C--see Figure 5. However, the
usable temperature range of the temperature sensor is 55
C to
+125
C. Figure 5 shows the OTR and how to set T
ALARM
(the
temperature at which the
OTI goes low).
OTR (Dec) = T
ALARM
(
C) + 103C
For example, to set T
ALARM
to 50
C, OTR = 50 + 103 = 153
Dec or 10011001 Bin. If the result of a temperature conversion
exceeds 50
C then OTI will go logic low. The OTI logic output
is reset high at the end of a serial read operation or if a new
temperature measurement is lower than T
ALARM
. The default
power on T
ALARM
is
50
C.
DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7
MSB
LSB
CONTROL BYTE
DB0
DB1
DB2
ADDRESS REGISTER
OVER-TEMPERATURE
REGISTER (OTR)
IF ANY BIT DB7 TO DB3 IS SET TO
A LOGIC '1' THEN THE FULL 8 BITS
OF THE CONTROL WORD ARE WRITTEN
TO THE OVER-TEMPERATURE REGISTER
IF DB7 TO DB3 ARE LOGIC '0'
THEN DB2 TO DB0 ARE WRITTEN
TO THE ADDRESS REGISTER
DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7
Figure 4. Address and Over-Temperature Register Selection
AD7816/AD7817/AD7818
10
REV. B
MSB
LSB
0
0
0
0
0
0
0
1
MINIMUM TEMPERATURE = 95C
1
1
1
1
1
1
1
1
MAXIMUM TEMPERATURE = +152C
OVER-TEMPERATURE REGISTER (DEC) = T
ALARM
+ 103 C
T
ALARM
RESOLUTION = 1 / LSB
OVER-TEMPERATURE REGISTER
DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7
Figure 5. The Over-Temperature Register (OTR)
CIRCUIT INFORMATION
The AD7817 and AD7818 are single- and four-channel, 9
s
conversion time, 10-bit A/D converters with on-chip tempera-
ture sensor, reference and serial interface logic functions on a
single chip. The AD7816 has no analog input channel and is
intended for temperature measurement only. The A/D converter
section consists of a conventional successive-approximation
converter based around a capacitor DAC. The AD7816,
AD7817, and AD7818 are capable of running on a 2.7 V to
5.5 V power supply and the AD7817 and AD7818 accept an
analog input range of 0 V to +V
REF
. The on-chip temperature
sensor allows an accurate measurement of the ambient device
temperature to be made. The working measurement range of
the Temperature Sensor is 55
C to +125C. The part requires
a 2.5 V reference, which can be provided from the part's own
internal reference or from an external reference source. The
on-chip reference is selected by connecting the REF
IN
pin to
analog ground.
CONVERTER DETAILS
Conversion is initiated by pulsing the
CONVST input. The
conversion clock for the part is internally generated so no exter-
nal clock is required except when reading from and writing to
the serial port. The on-chip track/hold goes from track-to-hold
mode and the conversion sequence is started on the falling edge
of the
CONVST signal. At this point the BUSY signal goes high
and low again 9
s or 27 s later (depending on whether an
analog input or the temperature sensor is selected) to indicate
the end of the conversion process. This signal can be used by a
microcontroller to determine when the result of the conversion
should be read. The track/hold acquisition time of the AD7817
and AD7818 is 400 ns.
A temperature measurement is made by selecting the Channel 0
of the on-chip MUX and carrying out a conversion on this
channel. A conversion on Channel 0 takes 27
s to complete.
Temperature measurement is explained in the Temperature
Measurement section of this data sheet.
The on-chip reference is not available to the user, but REF
IN
can be overdriven by an external reference source (2.5 V only).
The effect of reference tolerances on temperature measurements
is discussed in the section titled Temperature Measurement
Error Due to Reference Error.
All unused analog inputs should be tied to a voltage within the
nominal analog input range to avoid noise pickup. For mini-
mum power consumption, the unused analog inputs should be
tied to AGND.
TYPICAL CONNECTION DIAGRAM
Figure 6 shows a typical connection diagram for the AD7817.
The AGND and DGND are connected together at the device
for good noise suppression. The BUSY line is used to interrupt
the microcontroller at the end of the conversion process and the
serial interface is implemented using three wires--see Serial
Interface section for more details. An external 2.5 V reference
can be connected at the REF
IN
pin. If an external reference is
used, a 10
F capacitor should be connected between REF
IN
and AGND. For applications where power consumption is of
concern, the automatic power-down at the end of a conversion
should be used to improve power performance. See Power-
Down section of the data sheet.
VDD
AIN1
CONVST
AGND
DGND
REF
IN
SUPPLY
2.7V TO
5.5V
0.1 F
10 F
10 F
EXTERNAL
REFERENCE
OPTIONAL
EXTERNAL
REFERENCE
AD780/
REF-192
0V TO 2.5V
INPUT
D
OUT
RD/
WR
AIN2
AIN3
AIN4
D
IN
BUSY
OTI
C/ P
SCLK
THREE-WIRE
SERIAL
INTERFACE
CS
AD7817
Figure 6. Typical Connection Diagram
ANALOG INPUTS
Analog Input
Figure 7 shows an equivalent circuit of the analog input struc-
ture of the AD7817 and AD7818. The two diodes D1 and D2
provide ESD protection for the analog inputs. Care must be
taken to ensure that the analog input signal never exceeds the
supply rails by more than 200 mV. This will cause these diodes
to become forward biased and start conducting current into the
substrate. The maximum current these diodes can conduct
without causing irreversibly damage to the part is 20 mA. The
capacitor C2 in Figure 7 is typically about 4 pF and can mostly
be attributed to pin capacitance. The resistor R1 is a lumped
component made up of the on resistance of a multiplexer and a
switch. This resistor is typically about 1 k
. The capacitor C1 is
the ADC sampling capacitor and has a capacitance of 3 pF.
AD7816/AD7817/AD7818
11
REV. B
1.2V
REF
IN
SW1
2.5V
EXTERNAL
REFERENCE
DETECT
BUFFER
1.2V
26k
24k
Figure 9. On-Chip Reference
ADC TRANSFER FUNCTION
The output coding of the AD7816, AD7817, and AD7818 is
straight binary. The designed code transitions occur at succes-
sive integer LSB values (i.e., 1 LSB, 2 LSBs, etc.). The LSB
size is = 2.5 V/1024 = 2.44 mV. The ideal transfer characteristic
shown in Figure 10 below.
ANALOG INPUT
0V
1LSB
+2.5V1LSB
1LSB=2.5/1024
2.44mV
ADC CODE
111...111
111...110
111...000
011...111
000...010
000...001
000...000
Figure 10. ADC Transfer Function
TEMPERATURE MEASUREMENT
The on-chip temperature sensor can be accessed via multiplexer
Channel 0, i.e., by writing 0 0 0 to the Channel Address Regis-
ter. The temperature is also the power on default selection. The
transfer characteristic of the temperature sensor is shown in
Figure 11 below. The result of the 10-bit conversion on Chan-
nel 0 can be converted to degrees centigrade by using the fol-
lowing equation.
T
AMB
= 103
C + (ADC Code/4)
55C
125C
192Dec
912Dec
TEMPERATURE
ADC CODE
Figure 11. Temperature Sensor Transfer Characteristic
A
IN
D1
C1
3pF
V
DD
D2
C2
4pF
V
BALANCE
CONVERT PHASE - SWITCH OPEN
TRACK PHASE - SWITCH CLOSED
R1
1k
Figure 7. Equivalent Analog Input Circuit
DC Acquisition Time
The ADC starts a new acquisition phase at the end of a conver-
sion and ends on the falling edge of the
CONVST signal. At the
end of a conversion a settling time is associated with the sam-
pling circuit. This settling time lasts approximately 100 ns. The
analog signal on V
IN +
is also being acquired during this settling
time. Therefore, the minimum acquisition time needed is
approximately 100 ns.
Figure 8 shows the equivalent charging circuit for the sampling
capacitor when the ADC is in its acquisition phase. R2 repre-
sents the source impedance of a buffer amplifier or resistive
network, R1 is an internal multiplexer resistance and C1 is the
sampling capacitor.
V
IN
C1
3pF
R2
R1
1k
Figure 8. Equivalent Sampling Circuit
During the acquisition phase the sampling capacitor must be
charged to within a 1/2 LSB of its final value. The time it takes
to charge the sampling capacitor (T
CHARGE
) is given by the
following formula:
T
CHARGE
= 7.6
(R2 + 1 k) 3 pF
For small values of source impedance, the settling time associ-
ated with the sampling circuit (100 ns) is, in effect, the acquisi-
tion time of the ADC. For example with a source impedance (R2)
of 10
the charge time for the sampling capacitor is approxi-
mately 23 ns. The charge time becomes significant for source
impedances of 1 k
and greater.
AC Acquisition Time
In ac applications it is recommended to always buffer analog
input signals. The source impedance of the drive circuitry must
be kept as low as possible to minimize the acquisition time of
the ADC. Large values of source impedance will cause the THD
to degrade at high throughput rates.
ON-CHIP REFERENCE
The AD7816, AD7817, and AD7818 have an on-chip 1.2 V
bandgap reference that is gained up to give an output of 2.5 V.
The on-chip reference is selected by connecting the REF
IN
pin
to analog ground. This causes SW1 (see Figure 9) to open and
the reference amplifier to power up during a conversion. There-
fore the on-chip reference is not available externally. An external
2.5 V reference can be connected to the REF
IN
pin. This has the
effect of shutting down the on-chip reference circuitry and reduc-
ing I
DD
by about 0.25 mA.
AD7816/AD7817/AD7818
12
REV. B
For example, if the result of a conversion on Channel 0 was
1000000000 (512 Dec), the ambient temperature is equal to
103
C + (512/4) = +25C.
Table II below shows some ADC codes for various temperatures.
Table II. Temperature Sensor Output
ADC Code
Temperature
00 1100 0000
55
C
01 0011 1000
25
C
01 1001 1100
0
C
10 0000 0000
+25
C
10 0111 1000
+55
C
11 1001 0000
+125
C
TEMPERATURE MEASUREMENT ERROR DUE TO
REFERENCE ERROR
The AD7816, AD7817, and AD7818 are trimmed using a pre-
cision 2.5 V reference to give the transfer function described
previously. To show the effect of the reference tolerance on a
temperature reading, the temperature sensor transfer function
can be rewritten as a function of the reference voltage and the
temperature.
CODE (Dec) = ([113.3285
K T]/[q V
REF
] 0.6646) 1024
where
K = Boltzmann's Constant, 1.38
10
23
q = Charge on an electron, 1.6
10
19
T = Temperature (K)
So, for example, to calculate the ADC code at 25
C
CODE = ([113.3285
298 1.38 10
23
]/[1.6
10
19
2.5]
0.6646)
1024
= 511.5 (200 Hex)
As can be seen from the expression, a reference error will pro-
duce a gain error. This means that the temperature measure-
ment error due to reference error will be greater at higher
temperatures. For example, with a reference error of 1%, the
measurement error at 55
C would be 2.2 LSBs (0.5C) and
16 LSBs (4
C) at 125C.
SELF-HEATING CONSIDERATIONS
The AD7817 and AD7818 have an analog-to-digital conversion
function capable of a throughput rate of 100 kSPS. At this
throughput rate the AD7817 and AD7818 will consume between
4 mW and 6.5 mW of power. Because a thermal impedance is
associated with the IC package, the temperature of the die will
rise as a result of this power dissipation. The graphs below show
the self-heating effect in a 16-lead SOIC package. Figures 12
and 13 show the self-heating effect on a two-layer and four-layer
PCB. The plots were generated by assembling a heater (resistor)
and temperature sensor (diode) in the package being evaluated.
In Figure 12, the heater (6 mW) is turned off after 30 sec. The
PCB has little influence on the self-heating over the first few
seconds after the heater is turned on. This can be more clearly
seen in Figure 13 where the heater is switched off after 2 sec-
onds. Figure 14 shows the relative effects of self-heating in air,
fluid and in thermal contact with a large heat sink.
These diagrams represent the worst case effects of self-heating.
The heater delivered 6 mW to the interior of the package in all
cases. This power level is equivalent to the ADC continuously
converting at 100 kSPS. The effects of the self-heating can be
reduced at lower ADC throughput rates by operating on Mode
2--see Operating Modes section. When operating in this mode,
the on-chip power dissipation reduces dramatically and, as a
consequence, the self-heating effects.
TIME secs
TEMPERATURE
C
0.50
0.05
0
60
10
20
30
40
50
0.45
0.30
0.15
0.10
0.05
0.40
0.35
0.25
0.20
0.00
4-LAYER PCB
2-LAYER PCB
Figure 12. Self-Heating Effect Two-Layer and
Four-Layer PCB
TIME secs
TEMPERATURE
C
0.25
0.05
0
5
1
2
3
4
0.15
0.05
0.20
0.10
0.00
4-LAYER PCB
2-LAYER PCB
Figure 13. Self-Heating Effect Two-Layer and
Four-Layer PCB
AD7816/AD7817/AD7818
13
REV. B
DB0 DB7
DB0 - DB7(DB9)
D
OUT
CONVST
SCLK
BUSY
CS
RD/
WR
D
IN
OTI
t
2
t
1
t
17
t
15
t
16
t
3
Figure 16. Mode 1 Operation
TIME secs
TEMPERATURE
C
0.8
0.01
0
16
4
6
10
12
0.5
0.2
0.7
0.4
0.0
AIR
0.6
0.3
0.1
2
8
14
FLUID
HEATSINK
Figure 14. Self-Heating Effect in Air, Fluid and in Thermal
Contact with a Heatsink
TIME secs
TEMPERATURE
C
0.25
0.05
0.0
2.0
0.5
1.5
0.15
0.05
0.10
0.00
AIR
1.0
FLUID
HEATSINK
0.20
Figure 15. Self-Heating Effect in Air, Fluid and in Thermal
Contact with a Heatsink
OPERATING MODES
The AD7816, AD7817, and AD7818 have two possible modes
of operation depending on the state of the
CONVST pulse at
the end of a conversion.
Mode 1
In this mode of operation the
CONVST pulse is brought high
before the end of a conversion, i.e., before the BUSY goes low
(see Figure 16). When operating in this mode a new conversion
should not be initiated until 100 ns after the end of a serial read
operation. This quiet time is to allow the track/hold to accu-
rately acquire the input signal after a serial read.
Mode 2
When the AD7816, AD7817, and AD7818 are operated in Mode
2 (see Figure 17), they automatically power down at the end of
a conversion. The
CONVST is brought low to initiate a conver-
sion and is left logic low until after the end of the conversion.
At this point, i.e., when BUSY goes low, the devices will power-
down. The devices are powered up again on the rising edge of
the
CONVST signal. Superior power performance can be
achieved in this mode of operation by powering up the AD7816,
AD7817, and AD7818 only to carry out a conversion (see Power
vs. Throughput section).
AD7816/AD7817/AD7818
14
REV. B
THROUGHPUT kHz
10
1
0.01
0
80
10
POWER
mW
0.1
20
30
40
50
60
70
Figure 19. Power vs. Throughput Rate
AD7817 SERIAL INTERFACE
The serial interface on the AD7817 is a five-wire interface with
read and write capabilities, with data being read from the output
register via the D
OUT
line and data being written to the control
register via the D
IN
line. The part operates in a slave mode and
requires an externally applied serial clock to the SCLK input to
access data from the data register or write to the control byte.
The RD/
WR line is used to determine whether data is being
written to or read from the AD7817. When data is being written
to the AD7817, the RD/
WR line is set logic low and when data
is being read from the part the line is set logic high--see Figure
20. The serial interface on the AD7817 is designed to allow the
part to be interfaced to systems that provide a serial clock that is
synchronized to the serial data, such as the 80C51, 87C51,
68HC11, 68HC05, and PIC16Cxx microcontrollers.
DB0 DB7
DB0 DB7(DB9)
D
OUT
CONVST
SCLK
BUSY
CS
RD/
WR
D
IN
OTI
t
15
t
16
t
3
t
POWER-UP
t
1
Figure 17. Mode 2 Operation
POWER VS. THROUGHPUT
Superior power performance can be achieved by using the Auto-
matic Power-Down (Mode 2) at the end of a conversion--see
Operating Modes section of the data sheet.
t
POWER-UP
t
CONVERT
CONVST
BUSY
2 s
8 s
t
CYCLE
100ms @ 10kSPS
Figure 18. Automatic Power-Down
Figure 18 shows how the Automatic Power-Down is imple-
mented to achieve the optimum power performance from the
AD7816, AD7817, and AD7818. The devices are operated in
Mode 2 and the duration of
CONVST pulse is set to be equal to
the power-up time (2
s). As the throughput rate of the device is
reduced the device remains in its power-down state longer, and
the average power consumption over time drops accordingly.
For example, if the AD7817 is operated in a continuous sam-
pling mode with a throughput rate of 10 kSPS, the power con-
sumption is calculated as follows. The power dissipation during
normal operation is 4.8 mW, V
DD
= 3 V. If the power up time is
2
s and the conversion time is 9 s, the AD7817 can be said to
dissipate 4.8 mW typically for 11
s (worst case) during each
conversion cycle. If the throughput rate is 10 kSPS, the cycle
time is 100
s and the power dissipated while powered up dur-
ing each cycle is (11/100)
(4.8 mW) = 528 W typ. Power
dissipated while powered down during each cycle is (89/100)
(3 V
2 A) = 5.34 W typ. Overall power dissipated is 528 W
+ 5.34
W = 533 W.
AD7816/AD7817/AD7818
15
REV. B
Read Operation
Figure 20 shows the timing diagram for a serial read from the
AD7817.
CS is brought low to enable the serial interface and
RD/
WR is set logic high to indicate that the data transfer is a
serial read from the AD7817. The rising edge of RD/
WR clocks
out the first data bit (DB9), subsequent bits are clocked out on
the falling edge of SCLK and are valid on the rising edge. Ten
bits of data are transferred during a read operation. However,
the user has the choice of clocking only eight bits if the full ten
bits of the conversion result are not required. The serial data can
be accessed in a number of bytes if ten bits of data are being
read. However, RD/
WR must remain high for the duration of
the data transfer operation. Before starting a new data read
operation the RD/
WR signal must brought low and high again.
At the end of the read operation, the D
OUT
line enters a high
impedance state on the rising edge of the
CS or the falling edge
of RD/
WR, whichever occurs first.
Write Operation
Figure 20 also shows a control byte write operation to the
AD7817. The RD/
WR input goes low to indicate to the part
that a serial write is about to occur. The AD7817 control byte
is loaded on the rising edge of the first eight clock cycles of the
serial clock with data on all subsequent clock cycles being ignored.
To carry out a second successive write operation, the RD/
WR
signal must be brought high and low again.
Simplifying the Serial Interface
To minimize the number of interconnect lines to the AD7817,
the user can connect the
CS line to DGND. This is possible if
the AD7817 is not sharing the serial bus with another device. It
is also possible to tie the D
IN
and D
OUT
lines together. This
arrangement is compatible with the 8051 microcontroller. The
68HC11, 68HC05, and PIC16Cxx can be configured to operate
with a single serial data line. In this way the number of lines
required to operate the serial interface can be reduced to three,
i.e., RD/
WR, SCLK, and D
IN/OUT
--see Figure 6.
AD7816 AND AD7818 SERIAL INTERFACE MODE
The serial interface on the AD7816 and AD7818 is a three-wire
interface with read and write capabilities. Data is read from the
output register and the control byte is written to the AD7816
DB9
DB8
DB7
DB0
DB1
DB8
DB7
DB6
DB1
DB0
SCLK
D
IN
1
3
2
1
2
3
9
10
RD/
WR
CS
t
4
t
7
t
10
t
14a
t
14b
t
13
t
12
t
11
t
8
t
9
t
5
t
6
8
7
CONTROL BYTE
D
OUT
Figure 20. AD7817 Serial Interface Timing Diagram
and AD7818 via the D
IN/OUT
line. The part operates in a slave
mode and requires an externally applied serial clock to the
SCLK input to access data from the data register or write the
control byte. The RD/
WR line is used to determine whether
data is being written to or read from the AD7816 and AD7818.
When data is being written to the devices the RD/
WR line is set
logic low and when data is being read from the part the line is
set logic high--see Figure 21. The serial interface on the
AD7816 and AD7818 are designed to allow the part to be inter-
faced to systems that provide a serial clock that is synchronized
to the serial data, such as the 80C51, 87C51, 68HC11, 68HC05,
and PIC16Cxx microcontrollers.
Read Operation
Figure 21 shows the timing diagram for a serial read from the
AD7816 and AD7818. The RD/
WR is set logic high to indicate
that the data transfer is a serial read from the devices. When
RD/
WR is logic high the D
IN/OUT
pin becomes a logic output
and the first data bit (DB9) appears on the pin. Subsequent bits
are clocked out on the falling edge of SCLK, starting with the
second SCLK falling edge after RD/
WR goes high and are valid
on the rising edge of SCLK. Ten bits of data are transferred
during a read operation. However the user has the choice of
clocking only eight bits if the full ten bits of the conversion
result are not required. The serial data can be accessed in a
number of bytes if ten bits of data are being read; however,
RD/
WR must remain high for the duration of the data transfer
operation. To carry out a successive read operation the RD/
WR
pin must be brought logic low and high again. At the end of the
read operation, the D
IN/OUT
pin becomes a logic input on the
falling edge of RD/
WR.
Write Operation
A control byte write operation to the AD7816 and AD7818 is
also shown in Figure 21. The RD/
WR input goes low to indicate
to the part that a serial write is about to occur. The AD7816
and AD7818 control bytes are loaded on the rising edge of the
first eight clock cycles of the serial clock with data on all subse-
quent clock cycles being ignored. To carry out a successive write
to the AD7816 or AD7818 the RD/
WR pin must be brought
logic high and low again.
16
C0131608/00 (rev. B)
PRINTED IN U.S.A.
AD7816/AD7817/AD7818
REV. B
SCLK
1
3
2
1
2
3
9
10
RD/
WR
t
7
t
14a
t
13
t
12
t
11
t
8
t
9
t
5
t
6
8
7
CONTROL BYTE
DB9
DB8
DB7
DB0
DB1
DB0
DB1
DB8
DB7
DB6
D
IN
/D
OUT
Figure 21. AD7816/AD7818 Serial Interface Timing Diagram
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
16-Lead Thin Shrink Small Outline Package
(TSSOP) (RU-16)
16
9
8
1
0.201 (5.10)
0.193 (4.90)
0.256 (6.50)
0.246 (6.25)
0.177 (4.50)
0.169 (4.30)
PIN 1
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.0118 (0.30)
0.0075 (0.19)
0.0256
(0.65)
BSC
0.0433
(1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
0.028 (0.70)
0.020 (0.50)
8
0
8-Lead SOIC Package
(RM-8)
8
5
4
1
0.122 (3.10)
0.114 (2.90)
0.199 (5.05)
0.187 (4.75)
PIN 1
0.0256 (0.65) BSC
0.122 (3.10)
0.114 (2.90)
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.018 (0.46)
0.008 (0.20)
0.043 (1.09)
0.037 (0.94)
0.120 (3.05)
0.112 (2.84)
0.011 (0.28)
0.003 (0.08)
0.028 (0.71)
0.016 (0.41)
33
27
0.120 (3.05)
0.112 (2.84)
16-Lead Narrow Body (SOIC)
(R-16A)
16
9
8
1
0.3937 (10.00)
0.3859 (9.80)
0.2440 (6.20)
0.2284 (5.80)
0.1574 (4.00)
0.1497 (3.80)
PIN 1
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
0.0688 (1.75)
0.0532 (1.35)
0.0500
(1.27)
BSC
0.0099 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8
0
0.0196 (0.50)
0.0099 (0.25)
x 45
8-Lead Narrow Body (SOIC)
(SO-8)
0.1968 (5.00)
0.1890 (4.80)
8
5
4
1
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.0688 (1.75)
0.0532 (1.35)
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
0.0500
(1.27)
BSC
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8
0
0.0196 (0.50)
0.0099 (0.25)
x 45
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