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AD7818 [ADI]

Single- and 4-Channel, 9 us, 10-Bit ADCs with On-Chip Temperature Sensor; 单和4通道， 9我们， 10位ADC，片上温度传感器
AD7818
型号： AD7818
厂家： ADI    ADI
描述：

Single- and 4-Channel, 9 us, 10-Bit ADCs with On-Chip Temperature Sensor
单和4通道， 9我们， 10位ADC，片上温度传感器

传感器 温度传感器
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中文：  中文翻译
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Single- and 4-Channel, 9 ␮s, 10-Bit ADCs  
a
with On-Chip Temperature Sensor  
AD7816/AD7817/AD7818  
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  
V
REF  
DD  
IN  
AD7817  
OVER-TEMP  
REG  
OTI  
A > B  
A
B
TEMP  
SENSOR  
CHARGE  
REDISTRIBUTION  
DAC  
REF  
2.5V  
DATA  
OUT  
D
OUT  
Resolution of 0.25؇C  
V
IN1  
IN2  
IN3  
؎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  
V
V
MUX  
CONTROL  
LOGIC  
CONTROL  
REG  
SAMPLING  
CAPACITOR  
D
IN  
V
SCLK  
IN4  
RD/WR  
CLOCK  
V
BALANCE  
CS  
BUSY  
AGND  
DGND  
CONVST  
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  
The AD7816, AD7817 and AD7818 have a flexible serial inter-  
face that allows easy interfacing to most microcontrollers.  
The interface is compatible with the Intel 8051, Motorola  
SPI™ and QSPI™ protocols and National Semiconductors  
MICROWIRE™ protocol. For more information refer to the  
Serial Interface section of this data sheet.  
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  
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 (µSOIC).  
Automotive  
Battery Charging Applications  
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 +125°C.  
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 µs successive-approximation converter based around  
a capacitor DAC, an on-chip temperature sensor with an accu-  
racy of ±2°C, 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/  
µSOIC package.  
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 µW at 1 kSPS  
throughput rate.  
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 ±0.25°C. See Measuring Temperature section  
of the data sheet.  
SPI and QSPI are trademarks of Motorola, Inc.  
MICROWIRE is a trademark of National Semiconductor Corporation.  
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  
which may result from its use. No license is granted by implication or  
otherwise under any patent or patent rights of Analog Devices.  
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.  
Tel: 781/329-4700  
Fax: 781/326-8703  
World Wide Web Site: http://www.analog.com  
© Analog Devices, Inc., 2000  
AD7816/AD7817/AD7818  
AD7817–SPECIFICATIONS1  
(VDD = +2.7 V to +5.5 V, GND = 0 V, REFIN = +2.5 V unless otherwise noted)  
Parameter  
A Version *B Version *S Version Units  
Test Conditions/Comments  
DYNAMIC PERFORMANCE  
Sample Rate = 100 kSPS, Any  
Channel, fIN = 20 kHz  
Signal to (Noise + Distortion) Ratio2 58  
58  
–65  
–65  
58  
–65  
–65  
dB min  
dB max  
dB max  
Total Harmonic Distortion2  
Peak Harmonic or Spurious Noise2  
Intermodulation Distortion2  
Second Order Terms  
–65  
–65  
–75 dB typ  
–75 dB typ  
fa =19.9 kHz, fb = 20.1 kHz  
–67  
–67  
–80  
–67  
–67  
–80  
–67  
–67  
–80  
dB typ  
dB typ  
dB typ  
Third Order Terms  
Channel-to-Channel Isolation2  
fIN = 20 kHz  
Any Channel  
DC ACCURACY  
Resolution  
10  
10  
10  
Bits  
Minimum Resolution for Which  
No Missing Codes Are Guaranteed 10  
10  
±1  
±1  
±2  
±10  
±1/2  
±2  
10  
±1  
±1  
±2  
+20/–10  
±1/2  
±2  
Bits  
Relative Accuracy2  
Differential Nonlinearity2  
Gain Error2  
±1  
±1  
±2  
±10  
±1/2  
±2  
LSB max  
LSB max  
LSB max  
LSB max  
LSB max  
LSB max  
LSB max  
External Reference  
Internal Reference  
Gain Error Match2  
Offset Error2  
Offset Error Match  
±1/2  
±1/2  
±1/2  
TEMPERATURE SENSOR1  
Measurement Error  
Ambient Temperature +25°C  
TMIN to TMAX  
Measurement Error  
External Reference VREF = 2.5 V  
On-Chip Reference  
±2  
±3  
±1  
±2  
±2  
±3  
°C max  
°C max  
Ambient Temperature +25°C  
TMIN to TMAX  
Temperature Resolution  
±2.25  
±3  
1/4  
±2.25  
±3  
1/4  
±2.25  
±6  
1/4  
°C max  
°C max  
°C/LSB  
REFERENCE INPUT3, 4  
REFIN Input Voltage Range3  
2.625  
2.375  
40  
2.625  
2.375  
40  
2.625  
2.375  
40  
V max  
V min  
kΩ min  
pF max  
2.5 V + 5%  
2.5 V – 5%  
Input Impedance  
Input Capacitance  
10  
10  
10  
ON-CHIP REFERENCE5  
Nominal 2.5 V  
Temperature Coefficient3  
80  
80  
150  
400  
ppm/°C typ  
CONVERSION RATE  
Track/Hold Acquisition Time4  
Conversion Time  
400  
400  
ns max  
Source Impedance < 10 Ω  
Temperature Sensor  
Channels 1 to 4  
27  
9
27  
9
27  
9
µs max  
µs max  
POWER REQUIREMENTS  
VDD  
+5.5  
+2.7  
+5.5  
+2.7  
+5.5  
+2.7  
V max  
V min  
For Specified Performance  
IDD  
Logic Inputs = 0 V or VDD  
1.6 mA typ  
2.5 V External Reference Connected  
50 nA typ  
Normal Operation  
Using External Reference  
Power-Down  
2
1.75  
1
2
1.75  
1
2
1.75  
2
mA max  
mA max  
µA max  
Auto Power-Down Mode  
10 SPS Throughput Rate  
1 kSPS Throughput Rate  
10 kSPS Throughput Rate  
Power-Down  
VDD = 3 V  
6
6
6
µW typ  
µW typ  
µW typ  
µW max  
See Power vs. Throughput Section  
for Description of Power Dissipation  
in Auto Power-Down Mode  
Typically 0.15 µW  
60  
600  
3
60  
600  
3
60  
600  
6
–2–  
REV. A  
AD7816/AD7817/AD7818  
(VDD = +2.7 V to +5.5 V, GND = 0 V, REFIN = +2.5 V unless  
otherwise noted)  
AD7816/AD78186–SPECIFICATIONS1  
Parameter  
A Version  
Units  
Test Conditions/Comments  
DYNAMIC PERFORMANCE (AD7818 Only)  
Sample Rate = 100 kSPS, Any  
Channel, fIN = 20 kHz  
Signal to (Noise + Distortion) Ratio2  
Total Harmonic Distortion2  
Peak Harmonic or Spurious Noise2  
Intermodulation Distortion2  
Second Order Terms  
57  
–65  
–67  
dB min  
dB max  
dB typ  
–75 dB typ  
–75 dB typ  
fa = 19.9 kHz, fb = 20.1 kHz  
–67  
–67  
–80  
dB typ  
dB typ  
dB typ  
Third Order Terms  
Channel-to-Channel Isolation2  
fIN = 20 kHz  
Any Channel  
DC ACCURACY (AD7818 Only)  
Resolution  
10  
Bits  
Bits  
LSB max  
LSB max  
LSB max  
LSB max  
Minimum Resolution for Which  
No Missing Codes Are Guaranteed  
Relative Accuracy2  
10  
±1  
±1  
±10  
±4  
Differential Nonlinearity2  
Gain Error2  
Offset Error2  
TEMPERATURE SENSOR1  
Measurement Error  
Ambient Temperature +25°C  
TMIN to TMAX  
Measurement Error  
External Reference VREF = 2.5 V  
On-Chip Reference  
±2  
±3  
°C max  
°C max  
Ambient Temperature +25°C  
TMIN to TMAX  
Temperature Resolution  
±2  
±3  
1/4  
°C max  
°C max  
°C/LSB  
REFERENCE INPUT3, 4 (AD7816 Only)  
REFIN Input Voltage Range3  
2.625  
2.375  
50  
V max  
V min  
kΩ min  
pF max  
2.5 V + 5%  
2.5 V – 5%  
Input Impedance  
Input Capacitance  
10  
ON-CHIP REFERENCE5  
Nominal 2.5 V  
Temperature Coefficient3  
30  
ppm/°C typ  
CONVERSION RATE  
Track/Hold Acquisition Time4  
Conversion Time  
400  
ns max  
Source Impedance < 10 Ω  
Temperature Sensor  
Channel 1  
27  
9
µs max  
µs max  
(AD7818 Only)  
POWER REQUIREMENTS  
VDD  
+5.5  
+2.7  
V max  
V min  
For Specified Performance  
IDD  
Logic Inputs = 0 V or VDD  
1.3 mA typ  
2.5 V External Reference Connected  
500 nA typ  
Normal Operation  
Using External Reference  
Power-Down  
2
1.75  
2
mA max  
mA max  
µA max  
Auto Power-Down Mode  
10 SPS Throughput Rate  
1 kSPS Throughput Rate  
10 kSPS Throughput Rate  
Power-Down  
VDD = 3 V  
4
µW typ  
µW typ  
µW typ  
µW max  
See Power vs. Throughput Section for  
Description of Power Dissipation in  
Auto Power-Down Mode  
Typically 0.15 µW  
40  
400  
3
REV. A  
–3–  
AD7816/AD7817/AD7818–SPECIFICATIONS1  
Parameter  
A Version *B Version *S Version Units  
Test Conditions/Comments  
ANALOG INPUTS7  
Input Voltage Range  
(AD7817 and AD7818)  
VREF  
0
VREF  
0
VREF  
0
V max  
V min  
Input Leakage  
Input Capacitance  
±1  
10  
±1  
10  
±1  
10  
µA min  
pF max  
LOGIC INPUTS4  
Input High Voltage, VINH  
Input Low Voltage, VINL  
Input High Voltage, VINH  
Input Low Voltage, VINL  
Input Current, IIN  
2.4  
0.8  
2
0.4  
±3  
10  
2.4  
0.8  
2
0.4  
±3  
10  
2.4  
0.8  
2
0.4  
±3  
10  
V min  
V max  
V min  
V max  
µA max  
pF max  
VDD = 5 V ± 10%  
VDD = 5 V ± 10%  
VDD = 3 V ± 10%  
VDD = 3 V ± 10%  
Typically 10 nA, VIN = 0 V to VDD  
Input Capacitance, CIN  
LOGIC OUTPUTS4  
Output High Voltage, VOH  
ISOURCE = 200 µA  
VDD = 5 V ± 10%  
VDD = 3 V ± 10%  
ISINK = 200 µA  
4
2.4  
4
2.4  
4
2.4  
V min  
V min  
Output Low Voltage, VOL  
0.4  
0.2  
0.4  
0.2  
±1  
15  
0.4  
0.2  
±1  
15  
V max  
V max  
µA max  
pF max  
VDD = 5 V ± 10%  
VDD = 3 V ± 10%  
High Impedance Leakage Current ±1  
High Impedance Capacitance 15  
NOTES  
*B and S Versions apply to AD7817 only. For operating temperature ranges, see Ordering Guide.  
1AD7816 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 VDD = +2.7 V, TA = +85°C max and temperature sensor measurement error = ± 3°C.  
2See Terminology.  
3The 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.  
4Sample tested during initial release and after any redesign or process change that may affect this parameter.  
5On-chip reference shuts down when external reference is applied.  
6All specifications are typical for AD7818 at temperatures above +85°C and with VDD greater than +3.6 V.  
7Refers 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.  
V
V
REF  
DD  
DD  
IN  
AD7816  
AD7818  
OVER-TEMP  
REG  
OVER-TEMP  
REG  
A > B  
A
OTI  
A > B  
A
B
OTI  
B
TEMP  
SENSOR  
TEMP  
REF  
2.5V  
SENSOR  
CHARGE  
REDISTRIBUTION  
DAC  
CHARGE  
REDISTRIBUTION  
DAC  
REF  
2.5V  
DATA  
OUT  
DATA  
OUT  
D
D
V
OUT  
IN/  
OUT  
IN/  
MUX  
IN1  
MUX  
CONTROL  
LOGIC  
CONTROL  
LOGIC  
SAMPLING  
CAPACITOR  
SAMPLING  
CAPACITOR  
CONTROL  
REG  
CONTROL  
REG  
SCLK  
SCLK  
RD/WR  
CLOCK  
GENERATOR  
CLOCK  
RD/WR  
V
V
BALANCE  
BALANCE  
AGND  
CONVST  
AGND  
CONVST  
Figure 1. AD7816 Functional Block Diagram  
Figure 2. AD7818 Functional Block Diagram  
–4–  
REV. A  
AD7816/AD7817/AD7818  
(VDD = +2.7 V to +5.5 V, GND = 0 V, REFIN = +2.5 V. All specifications TMIN to TMAX unless  
otherwise noted)  
TIMING CHARACTERISTICS1, 2  
Parameter  
A, B Versions  
Units  
Test Conditions/Comments  
tPOWER-UP  
2
9
27  
20  
50  
0
µs max  
µs max  
µs max  
ns min  
Power-Up Time from Rising Edge of CONVST  
Conversion Time Channels 1 to 4  
Conversion Time Temperature Sensor  
CONVST Pulsewidth  
CONVST Falling Edge to BUSY Rising Edge  
CS Falling Edge to RD/WR Falling Edge Setup Time  
RD/WR Falling Edge to SCLK Falling Edge Setup  
DIN Setup Time before SCLK Rising Edge  
DIN Hold Time after SCLK Rising Edge  
t1a  
t1b  
t2  
t3  
t4  
t5  
t6  
t7  
t8  
ns max  
ns min  
ns min  
ns min  
ns min  
ns min  
ns min  
ns min  
ns min  
ns max  
ns max  
ns max  
ns max  
ns max  
ns min  
ns min  
0
10  
10  
40  
40  
0
SCLK Low Pulsewidth  
SCLK High Pulsewidth  
t9  
t10  
t11  
CS Falling Edge to RD/WR Rising Edge Setup Time  
RD/WR Rising Edge to SCLK Falling Edge Setup Time  
DOUT Access Time after RD/WR Rising Edge  
DOUT Access Time after SCLK Falling Edge  
DOUT Bus Relinquish Time after Falling Edge of RD/WR  
DOUT Bus Relinquish Time after Rising Edge of CS  
BUSY Falling Edge to OTI Falling Edge  
0
3
t12  
20  
20  
30  
30  
150  
40  
400  
3
t13  
3, 4  
t14a  
3, 4  
t14b  
t15  
t16  
t17  
RD/WR Rising Edge to OTI Rising Edge  
SCLK Rising Edge to CONVST Falling Edge (Acquisition Time of T/H)  
NOTES  
1Sample 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.  
2See Figures 16, 17, 20 and 21.  
3These figures are measured with the load circuit of Figure 3. They are defined as the time required for DOUT to cross 0.8 V or 2.4 V for VDD = 5 V ± 10% and 0.4 V  
or 2 V for VDD = 3 V ± 10%, as quoted on the specifications page of this data sheet.  
4These 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.  
I
200␮A  
OL  
TO  
OUTPUT  
PIN  
1.6V  
C
L
50pF  
200␮A  
I
OL  
Figure 3. Load Circuit for Access Time and Bus Relinquish Time  
REV. A  
–5–  
AD7816/AD7817/AD7818  
ABSOLUTE MAXIMUM RATINGS1  
µSOIC Package, Power Dissipation . . . . . . . . . . . . . . 450 mW  
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 206°C/W  
Lead Temperature, Soldering  
(
TA = +25°C unless otherwise noted)  
VDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V  
VDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V  
Analog Input Voltage to AGND  
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . +215°C  
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220°C  
VIN1 to VIN4 . . . . . . . . . . . . . . . . . . . –0.3 V to VDD + 0.3 V  
Reference Input Voltage to AGND2 . . . –0.3 V to VDD + 0.3 V  
Digital Input Voltage to DGND . . . . . . –0.3 V to VDD + 0.3 V  
Digital Output Voltage to DGND . . . . . –0.3 V to VDD + 0.3 V  
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C  
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . +150°C  
TSSOP, Power Dissipation . . . . . . . . . . . . . . . . . . . . 450 mW  
θJA 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  
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 100°C/W  
Lead Temperature, Soldering  
NOTES  
1Stresses 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.  
2If the Reference Input Voltage is likely to exceed VDD 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 REFIN pin and VDD pin. The  
diagram below shows how the diode should be connected.  
V
REF  
DD  
IN  
BAT81  
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . +215°C  
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220°C  
8-Lead SOIC Package, Power Dissipation . . . . . . . . . 450 mW  
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 157°C/W  
Lead Temperature, Soldering  
AD7816/AD7817  
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . +215°C  
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . +220°C  
ORDERING GUIDE  
Temperature  
Range  
Temperature  
Error @ +25°C  
Package  
Description  
Branding  
Information  
Package  
Options  
Model  
AD7816AR  
AD7816ARM  
–55°C to +125°C  
–55°C to +125°C  
±2°C  
±2°C  
8-Lead Narrow Body (SOIC)  
8-Lead µSOIC  
SO-8  
RM-8  
C4A  
AD7817AR  
AD7817BR  
AD7817ARU  
AD7817BRU  
AD7817SR  
–40°C to +85°C  
–40°C to +85°C  
–40°C to +85°C  
–40°C to +85°C  
–55°C to +125°C  
±2°C  
±1°C  
±2°C  
±1°C  
±2°C  
16-Lead Narrow Body (SOIC)  
16-Lead Narrow Body (SOIC)  
16-Lead (TSSOP)  
16-Lead (TSSOP)  
16-Lead Narrow Body (SOIC)  
R-16A  
R-16A  
RU-16  
RU-16  
R-16A  
AD7818AR  
AD7818ARM  
–55°C to +125°C  
–55°C to +125°C  
±2°C  
±2°C  
8-Lead Narrow Body (SOIC)  
8-Lead µSOIC  
SO-8  
RM-8  
C3A  
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.  
WARNING!  
ESD SENSITIVE DEVICE  
–6–  
REV. A  
AD7816/AD7817/AD7818  
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
3
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.  
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.  
OTI  
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
6
AGND  
REFIN  
Analog Ground. Ground reference for track/hold, comparator and capacitor DAC.  
Analog Input. An external 2.5 V reference can be connected to the AD7817 at this pin. To enable the on-  
chip reference the REFIN pin should be tied to AGND. If an external reference is connected to the  
AD7817, the internal reference will shut down.  
7–10  
V
IN1 to VIN4  
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 VREF. A channel is selected by writing to the Address Register of the AD7817—see Control  
Byte section.  
11  
12  
13  
VDD  
DGND  
DOUT  
Positive Supply Voltage, +2.7 V to +5.5 V.  
Digital Ground. Ground reference for digital circuitry.  
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  
15  
DIN  
SCLK  
Logic Input. Data is clocked into the AD7817 at this pin.  
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  
1
2
CONVST  
BUSY  
O T I  
16  
15  
RD/WR  
SCLK  
D
3
4
14  
13  
IN  
AD7817  
D
CS  
OUT  
TOP VIEW  
(Not to Scale)  
AGND  
5
6
DGND  
12  
11  
V
REF  
IN  
DD  
V
V
7
8
10  
9
IN4  
IN1  
V
V
IN3  
IN2  
REV. A  
–7–  
AD7816/AD7817/AD7818  
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  
VIN  
Analog and Digital Ground.  
4 (AD7818)  
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)  
REFIN  
Reference Input. An external 2.5 V reference can be connected to the AD7816 at this pin. To  
enable the on-chip reference the REFIN pin should be tied to AGND. If an external reference is  
connected to the AD7816, the internal reference will shut down.  
5
6
7
VDD  
DIN/OUT  
SCLK  
Positive supply voltage, +2.7 V to +5.5 V.  
Logic Input and Output. Serial data is clocked in and out of the AD7816/AD7818 at this pin.  
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  
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:  
SOIC/␮SOIC (AD7816)  
V22 +V32 +V42 +V52 +V62  
RD/WR  
CONVST  
1
8
THD (dB) = 20 log  
AD7816  
TOP VIEW  
(Not to Scale)  
SCLK  
OTI  
2
3
7
6
V1  
D
AGND  
IN/OUT  
where V1 is the rms amplitude of the fundamental and V2, V3,  
V4, V5 and V6 are the rms amplitudes of the second through the  
sixth harmonics.  
4
5
V
REF  
IN  
DD  
Peak Harmonic or Spurious Noise  
SOIC/␮SOIC (AD7818)  
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 fS/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.  
RD/WR  
CONVST  
1
8
AD7818  
TOP VIEW  
(Not to Scale)  
SCLK  
2
3
7
6
OTI  
D
AGND  
IN/OUT  
V
4
5
V
IN  
DD  
Intermodulation Distortion  
TERMINOLOGY  
Signal to (Noise + Distortion) Ratio  
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).  
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 (fS/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.  
–8–  
REV. A  
AD7816/AD7817/AD7818  
Address Register  
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.  
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).  
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.  
Table I. Channel Selection  
DB2  
DB1  
DB0  
Channel Selection  
Device  
0
0
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Temperature Sensor  
Channel 1  
Channel 2  
Channel 3  
Channel 4  
All  
AD7817/18  
AD7817  
AD7817  
AD7817  
Relative Accuracy  
Relative accuracy or endpoint nonlinearity is the maximum  
deviation from a straight line passing through the endpoints of  
the ADC transfer function.  
Internal Ref (1.23 V) All  
Over-Temperature Register  
Differential Nonlinearity  
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  
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.  
DB2  
DB1  
DB0 ADDRESS REGISTER  
Offset Error Match  
This is the difference in Offset Error between any two channels.  
IF DB7 TO DB3 ARE LOGIC '0'  
THEN DB2 TO DB0 ARE WRITTEN  
TO THE ADDRESS REGISTER  
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.  
LSB  
MSB  
DB7  
DB6  
DB5  
DB4  
DB3 DB2  
DB1  
DB0 CONTROL BYTE  
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  
Gain Error Match  
This is the difference in Gain Error between any two channels.  
Track/Hold Acquisition Time  
OVER-TEMPERATURE  
REGISTER (OTR)  
DB7  
DB6  
DB5  
DB4  
DB3  
DB2  
DB1  
DB0  
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 VIN 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 VIN before starting another conversion, to  
ensure that the part operates to specification.  
Figure 4. Address and Over-Temperature Register Selection  
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 +152°C—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 TALARM (the  
temperature at which the OTI goes low).  
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.  
OTR (Dec) = TALARM (°C) + 103°C  
For example, to set TALARM 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 TALARM. The default  
power on TALARM is 50°C.  
REV. A  
–9–  
AD7816/AD7817/AD7818  
OVER-TEMPERATURE REGISTER  
LSB  
DB0  
MSB  
DB7  
DB6  
DB5  
DB3  
DB2  
DB4  
DB1  
MINIMUM TEMPERATURE = –95°C  
MAXIMUM TEMPERATURE = +152°C  
0
1
0
1
0
1
0
1
1
1
0
1
0
1
0
1
OVER-TEMPERATURE REGISTER (DEC) = T  
+ 103؇C  
ALARM  
T
RESOLUTION = 1؇/ LSB  
ALARM  
Figure 5. The Over-Temperature Register (OTR)  
CIRCUIT INFORMATION  
TYPICAL CONNECTION DIAGRAM  
The AD7817 and AD7818 are single- and four-channel, 9 µs  
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 +VREF. 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 +125°C. 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 REFIN pin to analog  
ground.  
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 REFIN pin. If an external reference is  
used, a 10 µF capacitor should be connected between REFIN  
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.  
SUPPLY  
+2.7V TO  
+5.5V  
THREE-WIRE  
10␮F  
0.1␮F  
SERIAL  
INTERFACE  
V
DD  
SCLK  
AIN1  
RD/WR  
AIN2  
AIN3  
AIN4  
0V TO 2.5V  
INPUT  
D
OUT  
CONVERTER DETAILS  
D
␮C/␮P  
IN  
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 µs or 27 µs 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.  
AD7817  
CONVST  
AGND  
DGND  
BUSY  
OTI  
REF  
CS  
IN  
OPTIONAL  
EXTERNAL  
REFERENCE  
AD780/  
REF-192  
10␮F  
EXTERNAL  
REFERENCE  
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 kΩ. The capacitor C1 is  
the ADC sampling capacitor and has a capacitance of 3 pF.  
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 µs 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 REFIN  
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.  
–10–  
REV. A  
AD7816/AD7817/AD7818  
REF  
EXTERNAL  
REFERENCE  
DETECT  
V
IN  
DD  
D1  
C1  
3pF  
R1  
1k⍀  
1.2V  
A
V
IN  
BALANCE  
SW1  
C2  
4pF  
D2  
1.2V  
CONVERT PHASE - SWITCH OPEN  
TRACK PHASE - SWITCH CLOSED  
26
24
BUFFER  
2.5V  
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 VIN + is also being acquired during this settling  
time. Therefore, the minimum acquisition time needed is ap-  
proximately 100 ns.  
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 characteris-  
tic shown in Figure 10 below.  
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.  
111...111  
111...110  
R1  
1
V
IN  
R2  
111...000  
C1  
1LSB=2.5/1024  
2.44mV  
3pF  
011...111  
Figure 8. Equivalent Sampling Circuit  
000...010  
000...001  
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 (TCHARGE) is given by the  
following formula:  
000...000  
1LSB  
+2.5V•1LSB  
0V  
ANALOG INPUT  
Figure 10. ADC Transfer Function  
T
CHARGE = 7.6 × (R2 + 1 kΩ) × 3 pF  
TEMPERATURE MEASUREMENT  
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 Ω the charge time for the sampling capacitor is ap-  
proximately 23 ns. The charge time becomes significant for  
source impedances of 1 kΩ and greater.  
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.  
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.  
TAMB = –103°C + (ADC Code/4)  
125°C  
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 REFIN 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 ex-  
ternal +2.5 V reference can be connected to the REFIN pin.  
This has the effect of shutting down the on-chip reference cir-  
cuitry and reducing IDD by about 0.25 mA.  
–55°C  
192Dec  
912Dec  
ADC CODE  
Figure 11. Temperature Sensor Transfer Characteristic  
REV. A  
–11–  
AD7816/AD7817/AD7818  
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) = +25°C.  
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 seconds. Figure 14 shows the relative effects of self-  
heating in air, fluid and in thermal contact with a large heat  
sink.  
Table II below shows some ADC codes for various temperatures.  
Table II. Temperature Sensor Output  
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.  
ADC Code  
Temperature  
00 1100 0000  
01 0011 1000  
01 1001 1100  
10 0000 0000  
10 0111 1000  
11 1001 0000  
–55°C  
–25°C  
0°C  
+25°C  
+55°C  
+125°C  
0.50  
2-LAYER PCB  
TEMPERATURE MEASUREMENT ERROR DUE TO  
REFERENCE ERROR  
0.45  
0.40  
0.35  
0.30  
0.25  
The AD7816, AD7817 and AD7818 are trimmed using a preci-  
sion +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.  
0.20  
4-LAYER PCB  
0.15  
0.10  
CODE (Dec) = ([113.3285 × K × T]/[q × VREF] – 0.6646) × 1024  
0.05  
0.00  
where K = Boltzmann’s Constant, 1.38 × 10–23  
q = Charge on an electron, 1.6 × 10–19  
T = Temperature (K)  
–0.05  
0
10  
20  
30  
40  
50  
60  
TIME – secs  
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  
Figure 12. Self-Heating Effect Two-Layer and  
Four-Layer PCB  
= 511.5 (200 Hex)  
0.25  
0.20  
0.15  
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 (0.5°C) and  
+16 LSBs (4°C) at +125°C.  
0.10  
2-LAYER PCB  
4-LAYER PCB  
SELF-HEATING CONSIDERATIONS  
0.05  
0.00  
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 be-  
tween 4 mW and 6.5 mW of power. Because a thermal imped-  
ance 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  
–0.05  
0
1
2
3
4
5
TIME – secs  
Figure 13. Self-Heating Effect Two-Layer and  
Four-Layer PCB  
–12–  
REV. A  
AD7816/AD7817/AD7818  
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.  
0.8  
0.7  
0.6  
0.5  
0.4  
0.3  
0.2  
0.1  
0.0  
AIR  
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.  
FLUID  
HEATSINK  
–0.01  
Mode 2  
14  
0
2
4
6
8
10  
12  
16  
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).  
TIME – secs  
Figure 14. Self-Heating Effect in Air, Fluid and in Thermal  
Contact with a Heatsink  
0.25  
0.20  
FLUID  
AIR  
0.15  
HEATSINK  
0.10  
0.05  
0.00  
–0.05  
0.0  
0.5  
1.0  
1.5  
2.0  
TIME – secs  
Figure 15. Self-Heating Effect in Air, Fluid and in Thermal  
Contact with a Heatsink  
t1  
t2  
CONVST  
t3  
BUSY  
t17  
CS  
t15  
t16  
OTI  
RD/ WR  
SCLK  
D
IN  
DB0 – DB7  
DB0 - DB7(DB9)  
D
OUT  
Figure 16. Mode 1 Operation  
REV. A  
–13–  
AD7816/AD7817/AD7818  
tPOWER-UP  
t1  
CONVST  
t3  
BUSY  
CS  
t15  
OTI  
RD/ WR  
SCLK  
t16  
D
IN  
DB0 – DB7  
DB0 – DB7(DB9)  
D
OUT  
Figure 17. Mode 2 Operation  
10  
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.  
1
tPOWER-UP  
tCONVERT  
2␮s  
8␮s  
CONVST  
0.1  
BUSY  
tCYCLE  
100ms @ 10kSPS  
0.01  
0
10  
20  
30  
40  
50  
60  
70  
80  
THROUGHPUT – kHz  
Figure 18. Automatic Power-Down  
Figure 19. Power vs. Throughput Rate  
AD7817 SERIAL INTERFACE  
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 µs). 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.  
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 DOUT line and data being written to the control  
register via the DIN 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.  
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 6 mW, VDD = 3 V. If the power up time is  
2 µs and the conversion time is 9 µs, the AD7817 can be said to  
dissipate 6 mW typically for 11 µs (worst case) during each  
conversion cycle. If the throughput rate is 10 kSPS, the cycle  
time is 100 µs and the power dissipated during each cycle is  
(11/100) × (6 mW) = 600 µW typ.  
–14–  
REV. A  
AD7816/AD7817/AD7818  
CS  
t4  
t10  
RD/WR  
t5  
t11  
t8  
7
SCLK  
1
2
3
8
1
2
3
9
10  
t6  
t9  
t7  
DB1  
D
DB6  
CONTROL BYTE  
DB0  
DB8  
DB7  
IN  
t14b  
t12  
t13  
t14a  
D
DB9  
DB1  
DB0  
DB8  
DB7  
OUT  
Figure 20. AD7817 Serial Interface Timing Diagram  
Read Operation  
and AD7818 via the DIN/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.  
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 DOUT line enters a high  
impedance state on the rising edge of the CS or the falling edge  
of RD/WR, whichever occurs first.  
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 DIN/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 DIN/OUT pin becomes a logic input on the  
falling edge of RD/WR.  
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 ig-  
nored. 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 DIN and DOUT 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 DIN/OUT—see Figure 6.  
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.  
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  
REV. A  
–15–  
AD7816/AD7817/AD7818  
RD/WR  
t5  
t11  
t8  
7
1
2
3
8
1
2
3
9
10  
SCLK  
t6  
t9  
t14a  
t12  
t13  
t7  
DB1  
DB0  
D
/D  
DB6  
CONTROL BYTE  
DB8  
DB7  
IN OUT  
DB9  
DB8  
DB7  
DB1  
DB0  
Figure 21. AD7816/AD7818 Serial Interface Timing Diagram  
OUTLINE DIMENSIONS  
Dimensions shown in inches and (mm).  
16-Lead Narrow Body (SOIC)  
(R-16A)  
16-Lead Thin Shrink Small Outline Package  
(TSSOP) (RU-16)  
0.201 (5.10)  
0.193 (4.90)  
0.3937 (10.00)  
0.3859 (9.80)  
16  
9
16  
1
9
8
0.1574 (4.00)  
0.2440 (6.20)  
0.2284 (5.80)  
0.1497 (3.80)  
1
8
0.0688 (1.75)  
0.0532 (1.35)  
PIN 1  
0.0196 (0.50)  
0.0099 (0.25)  
x 45°  
0.0098 (0.25)  
0.0040 (0.10)  
PIN 1  
0.006 (0.15)  
0.002 (0.05)  
0.0433  
(1.10)  
MAX  
8°  
0°  
0.0500  
(1.27)  
BSC  
0.0192 (0.49)  
0.0138 (0.35)  
SEATING  
PLANE  
0.0500 (1.27)  
0.0160 (0.41)  
0.0099 (0.25)  
0.0075 (0.19)  
0.028 (0.70)  
0.020 (0.50)  
8°  
0°  
0.0118 (0.30)  
0.0075 (0.19)  
0.0256  
(0.65)  
BSC  
SEATING  
PLANE  
0.0079 (0.20)  
0.0035 (0.090)  
8-Lead Narrow Body (SOIC)  
(SO-8)  
8-Lead ␮SOIC Package  
(RM-8)  
0.1968 (5.00)  
0.1890 (4.80)  
0.122 (3.10)  
0.114 (2.90)  
8
1
5
4
0.1574 (4.00)  
0.1497 (3.80)  
5
4
0.2440 (6.20)  
0.2284 (5.80)  
8
1
0.199 (5.05)  
0.187 (4.75)  
0.122 (3.10)  
0.114 (2.90)  
PIN 1  
0.0688 (1.75)  
0.0532 (1.35)  
0.0196 (0.50)  
x 45°  
0.0098 (0.25)  
0.0040 (0.10)  
0.0099 (0.25)  
PIN 1  
0.0256 (0.65) BSC  
0.120 (3.05)  
0.112 (2.84)  
0.120 (3.05)  
8°  
0°  
0.0500  
(1.27)  
BSC  
0.0192 (0.49)  
0.0138 (0.35)  
0.112 (2.84)  
SEATING  
PLANE  
0.0098 (0.25)  
0.0075 (0.19)  
0.0500 (1.27)  
0.0160 (0.41)  
0.043 (1.09)  
0.037 (0.94)  
0.006 (0.15)  
0.002 (0.05)  
33°  
27°  
0.018 (0.46)  
0.011 (0.28)  
0.003 (0.08)  
0.028 (0.71)  
0.016 (0.41)  
SEATING  
PLANE  
0.008 (0.20)  
–16–  
REV. A  

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