4-Channel/Single-Channel, 9 μs,
10-Bit ADCs with On-Chip Temperature Sensor
Data Sheet AD7817/AD7818
Rev. E Document Feedback
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FEATURES
10-bit ADC with 9 μs conversion time
1 AD7818 and 4 AD7817 single-ended analog input channels
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%)
Overtemperature indicator
Automatic power-down at the end of a conversion
Low power operation
4 μW at a throughput rate of 10 SPS
40 μW at a throughput rate of 1 kSPS
400 μW at a throughput rate of 10 kSPS
Flexible serial interface
APPLICATIONS
Data acquisition systems with ambient temperature
monitoring
Industrial process control
Automotive
Battery charging applications
FUNCTIONAL BLOCK DIAGRAMS
AD7817
TEMP
SENSOR
V
IN1
V
IN2
V
IN3
V
IN4
MUX
AGND DGND
V
BALANCE
SAMPLING
CAPACITOR
REF
2.5V
REF
IN
OTI
D
OUT
D
IN
SCLK
RD/WR
CS
V
DD
BUSY CONVST
CLOCK
REG
CONTROL
CONTROL
LOGIC
DATA
OUT
A
B
OVERTEMP
REG
CHARGE
REDISTRIBUTION
DAC
A > B
01316-001
Figure 1. AD7817 Functional Block Diagram
AD7818
TEMP
SENSOR
V
IN1
MUX
AGND
V
BALANCE
SAMPLING
CAPACITOR
REF
2.5V
OTI
D
IN/OUT
SCLK
RD/WR
V
DD
CONVST
CLOCK
GENERATOR
CONTROL
REG
CONTROL
LOGIC
DATA
OUT
A
B
OVERTEMP
REG
CHARGE
REDISTRIBUTION
DAC
A > B
01316-002
Figure 2. AD7818 Functional Block Diagram
GENERAL DESCRIPTION
The AD7817/AD7818 are 10-bit, single- and 4-channel analog-to-
digital converters (ADCs) with an on-chip temperature sensor that
can operate from a single 2.7 V to 5.5 V power supply. Each
device contains a 9 µs successive approximation converter based
around a capacitor digital-to-analog converter (DAC), an on-
chip temperature sensor with an accuracy of ±2°C, an on-chip
clock oscillator, inherent track-and-hold functionality, and an
on-chip reference (2.5 V).
The on-chip temperature sensor of the AD7817/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 the Temperature Measurement section.
The AD7817/AD7818 have a flexible serial interface that allows
easy interfacing to most microcontrollers. The interface is
compatible with the Intel 8051, Motorola SPI and QSPI, and
National Semiconductors MICROWIRE protocols. For more
information, refer to the AD7817 Serial Interface section and
the AD7818 Serial Interface Mode section.
The AD7817 is available in a narrow body, 0.15 inch, 16-lead
SOIC and a 16-lead TSSOP, and the AD7818 comes in an 8-lead
SOIC and an 8-lead MSOP.
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.
2. An overtemperature 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 overtemperature
register. The overtemperature indicator pin goes logic low
when a predetermined temperature is exceeded.
3. The automatic power-down feature enables the AD7817 and
AD7818 to achieve superior power performance at slower
throughput rates, that is, 40 µW at 1 kSPS throughput rate.
AD7817/AD7818 Data Sheet
Rev. E | Page 2 of 20
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Functional Block Diagrams ............................................................. 1
General Description ......................................................................... 1
Product Highlights ........................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Timing Characteristics ................................................................ 6
Absolute Maximum Ratings ............................................................ 7
ESD Caution .................................................................................. 7
Pin Configurations and Function Descriptions ........................... 8
Terminology .................................................................................... 10
Control Byte .................................................................................... 11
Circuit Information .................................................................... 12
Converter Details ....................................................................... 12
Typical Connection Diagram ................................................... 12
Analog Inputs ............................................................................. 12
On-Chip Reference .................................................................... 13
ADC Transfer Function ............................................................. 13
Temperature Measurement ....................................................... 14
Temperature Measurement Error Due to Reference Error ... 14
Self-Heating Considerations ..................................................... 14
Operating Modes ........................................................................ 15
Power vs. Throughput................................................................ 17
AD7817 Serial Interface ............................................................. 17
AD7818 Serial Interface Mode ................................................. 18
Outline Dimensions ....................................................................... 19
Ordering Guide .......................................................................... 20
REVISION HISTORY
11/15—Rev. D to Rev. E
Changes to Title, Figure 1, and Figure 2 ........................................ 1
Change to Temperature Sensor (AD7818 Only) Parameter,
Table 1 ................................................................................................ 4
Change to Power Requirements (AD7818 Only) Parameter,
Table 1 ................................................................................................ 5
10/12—Rev. C to Rev. D
Deleted AD7816.................................................................. Universal
Changes to Format ............................................................. Universal
Deleted Figure 15; Renumbered Sequentially ............................ 14
Updated Outline Dimensions ....................................................... 19
Changes to Ordering Guide .......................................................... 20
9/04—Rev. B to Rev. C
Changes to Ordering Guide ............................................................. 6
Changes to Operating Modes Section and Figure 16 ................ 13
Changes to Figure 17 ...................................................................... 14
Changes to AD7817 Serial Interface, Read Operation Section
and Figure 20 ................................................................................... 15
Changes to Figure 21 ...................................................................... 16
Data Sheet AD7817/AD7818
Rev. E | Page 3 of 20
SPECIFICATIONS
VDD = 2.7 V to 5.5 V, GND = 0 V, REFIN = 2.5 V, unless otherwise noted. The AD7817 temperature sensor is specified with an external
2.5 V reference, and the AD7818 temperature sensor is specified with an on-chip reference. For VDD = 2.7 V, TA = 85°C maximum and
temperature sensor measurement error = ±3°C.
Table 1.
Parameter A Version1 B Version1 S Version1 Unit Test Conditions/Comments
DYNAMIC PERFORMANCE (AD7817 ONLY) Sample rate = 100 kSPS, any channel,
fIN = 20 kHz
Signal-to-(Noise + Distortion) Ratio2 58 58 58 dB min
Total Harmonic Distortion2 –65 −65 −65 dB max −75 dB typical
Peak Harmonic or Spurious Noise2 –65 −65 −65 dB max −75 dB typical
Intermodulation Distortion2 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 Isolation2 –80 −80 −80 dB typ fIN = 20 kHz
DC ACCURACY (AD7817 ONLY) Any channel
Resolution 10 10 10 Bits
Minimum Resolution for Which No
Missing Codes are Guaranteed
10 10 10
Relative Accuracy2 ±1 ±1 ±1 LSB max
Differential Nonlinearity2 ±1 ±1 ±1 LSB max
Gain Error2 ±2 ±2 ±2 LSB max External reference
±10 ±10 +20/−10 LSB max Internal reference
Gain Error Match2 ±1/2 ±1/2 ±1/2 LSB max
Offset Error2 ±2 ±2 ±2 LSB max
Offset Error Match ±1/2 ±1/2 ±1/2 LSB max
TEMPERATURE SENSOR (AD7817 ONLY)
Measurement Error External reference VREF = 2.5 V
Ambient Temperature 25°C ±2 ±1 ±2 °C max
TMIN to TMAX ±3 ±2 ±3 °C max
Measurement Error On-chip reference
Ambient Temperature 25°C ±2.25 ±2.25 ±2.25 °C max
TMIN to TMAX ±3 ±3 ±6 °C max
Temperature Resolution 1/4 1/4 1/4 °C/LSB
REFERENCE INPUT (AD7817 ONLY)3, 4
REFIN Input Voltage Range3 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 kΩ min
Input Capacitance 10 10 10 pF max
ON-CHIP REFERENCE (AD7817 ONLY)5 Nominal 2.5 V
Temperature Coefficient3 80 80 150 ppm/°C typ
CONVERSION RATE (AD7817 ONLY)
Track-and-Hold Acquisition Time4 400 400 400 ns max Source Impedance < 10 Ω
Conversion Time
Temperature Sensor 27 27 27 µs max
Channel 1 to Channel 4 9 9 9 s max
AD7817/AD7818 Data Sheet
Rev. E | Page 4 of 20
Parameter A Version1 B Version1 S Version1 Unit Test Conditions/Comments
POWER REQUIREMENTS (AD7817 ONLY)
VDD 5.5 5.5 5.5 V max For specified performance
2.7 2.7 2.7 V min
IDD Logic inputs = 0 V or VDD
Normal Operation 2 2 2 mA max 1.6 mA typical
Using External Reference 1.75 1.75 1.75 mA max 2.5 V external reference connected
Power-Down (VDD = 5 V) 10 10 12.5 μA max 5.5 μA typical
Power-Down (VDD = 3 V) 4 4 4.5 μA max 2 μA typical
Auto Power-Down Mode VDD = 3 V
10 SPS Throughput Rate 6.4 6.4 6.4 μW typ See the Power vs. Throughput
section for description of power
dissipation in auto power-down mode
1 kSPS Throughput Rate 48.8 48.8 48.8 μW typ
10 kSPS Throughput Rate 434 434 434 μW typ
Power-Down 12 12 13.5 μW max Typically 6 μW
DYNAMIC PERFORMANCE (AD7818 ONLY)6 Sample rate = 100 kSPS, any channel,
fIN = 20 kHz
Signal-to-(Noise + Distortion) Ratio2 57 dB min
Total Harmonic Distortion2 –65 dB max −75 dB typical
Peak Harmonic or Spurious Noise2 –67 dB typ −75 dB typical
Intermodulation Distortion2 fa = 19.9 kHz, fb = 20.1 kHz
Second-Order Terms –67 dB typ
Third-Order Terms –67 dB typ
Channel-to-Channel Isolation2 –80 dB typ fIN = 20 kHz
DC ACCURACY (AD7818 ONLY)6 Any channel
Resolution 10 Bits
Minimum Resolution for Which No
Missing Codes are Guaranteed
10 Bits
Relative Accuracy2 ±1 LSB max
Differential Nonlinearity2 ±1 LSB max
Gain Error2 ±10 LSB max
Offset Error2 ±4 LSB max
TEMPERATURE SENSOR (AD7818 ONLY)6
Measurement Error Internal reference VREF = 2.5 V
Ambient Temperature 25°C ±2 °C max
TMIN to TMAX ±3 °C max
Measurement Error On-chip reference
Ambient Temperature 25°C ±2 °C max
TMIN to TMAX ±3 °C max
Temperature Resolution 1/4 °C/LSB
ON-CHIP REFERENCE (AD7818 ONLY)5 Nominal 2.5 V
Temperature Coefficient3 30 ppm/°C typ
CONVERSION RATE (AD7818 ONLY)6
Track-and-Hold Acquisition Time4 400 ns max Source impedance < 10 Ω
Conversion Time
Temperature Sensor 27 μs max
Channel 1 9 μs max
Data Sheet AD7817/AD7818
Rev. E | Page 5 of 20
Parameter A Version1 B Version1 S Version1 Unit Test Conditions/Comments
POWER REQUIREMENTS (AD7818 ONLY)6
VDD 5.5 V max For specified performance
2.7 V min
IDD Logic inputs = 0 V or VDD
Normal Operation 2 mA max 1.3 mA typical
Using External Reference 1.75 mA max 2.5 V internal reference connected
Power-Down (VDD = 5 V) 10.75 µA max 6 µA typ
Power-Down (VDD = 3 V) 4.5 µA max 2 µA typ
Auto Power-Down Mode VDD = 3 V
10 SPS Throughput Rate 6.4 µW typ See the Power vs. Throughput section
for description of power dissipation
in auto power-down mode
1 kSPS Throughput Rate 48.8 µW typ
10 kSPS Throughput Rate 434 µW typ
Power-Down 13.5 µW max Typically 6 µW
ANALOG INPUTS (AD7817/AD7818)7
Input Voltage Range VREF VREF VREF V max
0 0 0 V min
Input Leakage ±1 ±1 ±1 µA min
Input Capacitance 10 10 10 pF max
LOGIC INPUTS (AD7817/AD7818)4
Input High Voltage, VINH 2.4 2.4 2.4 V min VDD = 5 V ±10%
Input Low Voltage, VINL 0.8 0.8 0.8 V max VDD = 5 V ±10%
Input High Voltage, VINH 2 2 2 V min VDD = 3 V ±10%
Input Low Voltage, VINL 0.4 0.4 0.4 V max VDD = 3 V ±10%
Input Current, IIN ±3 ±3 ±3 µA max Typically 10 nA, VIN = 0 V to VDD
Input Capacitance, CIN 10 10 10 pF max
LOGIC OUTPUTS (AD7817/AD7818)4
Output High Voltage, VOH ISOURCE = 200 µA
4 4 4 V min VDD = 5 V ± 10%
2.4 2.4 2.4 V min VDD = 3 V ± 10%
Output Low Voltage, VOL ISINK = 200 µA
0.4 0.4 0.4 V max VDD = 5 V ± 10%
0.2 0.2 0.2 V max VDD = 3 V ± 10%
High Impedance Leakage Current ±1 ±1 ±1 µA max
High Impedance Capacitance 15 15 15 pF max
1 The B Version and the S Version only apply to the AD7817. The A Version applies to the AD7817 or the AD7818 (as stated in specification).
2 See Terminology.
3 The accuracy of the temperature sensor is affected by reference tolerance. The relationship between the two is explained in the Temperature Measurement Error Due
to Reference Error section.
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 These specifications are typical for AD7818 at temperatures above 85°C and with VDD greater than 3.6 V.
7 This refers to the input current when the part is not converting. Primarily due to the reverse leakage current in the ESD protection diodes.
AD7817/AD7818 Data Sheet
Rev. E | Page 6 of 20
TIMING CHARACTERISTICS
VDD = 2.7 V to 5.5 V, GND = 0 V, REFIN = 2.5 V. All specifications TMIN to TMAX, unless otherwise noted. Sample tested during initial
release and after any redesign or process changes that may affect the parameters. 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. See Figure 17, Figure 18, Figure 21, and Figure 22.
Table 2.
Parameter A Version/B Version Unit Test Conditions/Comments
tPOWER-UP 2 µs max Power-up time from rising edge of CONVST
t1a 9 µs max Conversion time Channel 1 to Channel 4
t1b 27 µs max Conversion time temperature sensor
t2 20 ns min CONVST pulse width
t3 50 ns max CONVST falling edge to BUSY rising edge
t4 0 ns min CS falling edge to RD/WR falling edge setup time
t5 0 ns min RD/WR falling edge to SCLK falling edge setup
t6 10 ns min DIN setup time before SCLK rising edge
t7 10 ns min DIN hold time after SCLK rising edge
t8 40 ns min SCLK low pulse width
t9 40 ns min SCLK high pulse width
t10 0 ns min CS falling edge to RD/WR rising edge setup time
t11 0 ns min RD/WR rising edge to SCLK falling edge setup time
t121 20 ns max DOUT access time after RD/WR rising edge
t131 20 ns max DOUT access time after SCLK falling edge
t14a1, 2 30 ns max DOUT bus relinquish time after falling edge of RD/WR
t14b1, 2 30 ns max DOUT bus relinquish time after rising edge of CS
t15 150 ns max BUSY falling edge to OTI falling edge
t16 40 ns min RD/WR rising edge to OTI rising edge
t17 400 ns min SCLK rising edge to CONVST falling edge (acquisition time of T/H)
1 These 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 shown in Table 1.
2 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 the external bus loading capacitances.
200µA I
OL
200µA I
OL
1.6V
TO OUTPUT
PIN C
L
50pF
01316-003
Figure 3. Load Circuit for Access Time and Bus Relinquish Time
Data Sheet AD7817/AD7818
Rev. E | Page 7 of 20
ABSOLUTE MAXIMUM RATINGS
TA = 25°C unless otherwise noted.
Table 3.
Parameter Rating
VDD to AGND −0.3 V to +7 V
VDD to DGND −0.3 V to +7 V
Analog Input Voltage to AGND
VIN1 to VIN4 −0.3 V to VDD + 0.3 V
Reference Input Voltage to AGND1 −0.3 V to VDD + 0.3V
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
16-Lead 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
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
Vapor Phase (60 sec) 215°C
Infrared (15 sec) 220°C
8-Lead MSOP Package, Power Dissipation 450 mW
θJA Thermal Impedance 206°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) 215°C
Infrared (15 sec) 220°C
1 If the reference input voltage is likely to exceed VDD by more than 0.3 V (that
is, 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.
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
ESD CAUTION
AD7817/AD7818 Data Sheet
Rev. E | Page 8 of 20
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
1
2
3
4
5
6
7
8
BUSY
OTI
CS
V
IN1
REF
IN
AGND
C
ONVST
V
IN2
16
15
14
13
12
11
10
9
SCLK
D
IN
D
OUT
V
IN4
V
IN3
V
DD
DGND
RD/WR
AD7817
TOP VIEW
(Not to Scale)
01316-004
Figure 4. AD7817 Pin Configuration
Table 4. AD7817 Pin Function Descriptions
Pin
No. 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 track-and-hold in hold mode. Track-and-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 powers down. See the Operating Modes section.
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 overtemperature indicator (OTI) is set logic low if the result of a conversion on Channel 0
(temperature sensor) is greater that an 8-bit word in the overtemperature register (OTR). The signal is reset at the end
of a serial read operation, that is, 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 necessary if the AD7817
is sharing the serial bus with more than one device.
5 AGND Analog Ground. Ground reference for track-and-hold comparator and capacitor DAC.
6 REFIN Analog Input. An external 2.5 V reference can be connected to the AD7817 at this pin. To enable the on-chip reference,
tie the REFIN pin to AGND. If an external reference is connected to the AD7817, the internal reference shuts down.
7
to
10
VIN1 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 the Control Byte section.
11 VDD Positive Supply Voltage, 2.7 V to 5.5 V.
12 DGND Digital Ground. Ground reference for digital circuitry.
13 DOUT 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 DIN 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. Set the RD/WR logic high for a read operation and logic low for a write operation.
Data Sheet AD7817/AD7818
Rev. E | Page 9 of 20
AD7818
TOP VIEW
(Not to Scale)
CONVST
1
OTI
2
GND
3
V
IN 4
RD/WR
8
SCLK
7
D
IN/OUT
6
V
DD
5
01316-005
Figure 5. AD7818 Pin Configuration
Table 5. AD7818 Pin Function Descriptions
Pin
No. Mnemonic Description
1 CONVST Logic Input Signal. The convert start signal initiates a 10-bit analog-to-digital conversion on the falling edge of this
signal. The falling edge of this signal places track-and-hold in hold mode. Track-and-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
AD7818 powers down. See the Operating Modes section.
2 OTI Logic Output. The overtemperature indicator (OTI) is set logic low if the result of a conversion on Channel 0
(temperature sensor) is greater that an 8-bit word in the overtemperature register (OTR). The signal is reset at the end
of a serial read operation, that is, a rising RD/WR edge.
3 GND Analog and Digital Ground.
4 VIN 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 the
Control Byte section.
5 VDD Positive Supply Voltage, 2.7 V to 5.5 V.
6 DIN/OUT Logic Input and Output. Serial data is clocked in and out of the 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 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 AD7818 whether the next data transfer operation is a read
or a write. Set the RD/WR logic high for a read operation and logic low for a write.
AD7817/AD7818 Data Sheet
Rev. E | Page 10 of 20
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 nonfundamental
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) = (6.02N + 1.76) dB
Thus, for a 10-bit converter, this is 62 dB.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the fundamental.
For the AD7817/AD7818, it is defined as:
1
2
6
2
5
2
4
2
3
2
2
log20 V
VVVVV
dBTHD
where:
V1 is the rms amplitude of the fundamental.
V2, V3, V4, V5, and V6 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 fS/2 and excluding dc) to the rms value of
the fundamental. Normally, the value of this specification is
determined by the largest harmonic in the spectrum; however,
for devices where the harmonics are buried in the noise floor, it
is a noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities creates 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 − ), while the third-order terms
include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb).
The AD7817/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 intermodulation
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 determining 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.
Gain Error
This is the deviation of the last code transition (1111 . . . 110) to
(1111 . . . 111) from the ideal, that is, 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.
Offset Error
This is the deviation of the first code transition (0000 . . . 000) to
(0000 . . . 001) from the ideal, that is, AGND + 1 LSB.
Offset Error Match
This is the difference in offset error between any two channels.
Track-and-Hold Acquisition Time
The track-and-hold acquisition time is the time required for the
output of the track-and-hold amplifier to reach its final value,
within ±1/2 LSB, after the end of conversion (the point at which
the track-and-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 the AD7818.
It means that the user must wait for the duration of the track-
and-hold acquisition time after the end of conversion or after a
channel change/step input change to VIN before starting another
conversion, to ensure that the device operates to specification.
Data Sheet AD7817/AD7818
Rev. E | Page 11 of 20
CONTROL BYTE
The AD7817/AD7818 contain two on-chip registers, the
address register and the overtemperature 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 AD7817/AD7818 is transferred to one of the two on-chip
registers as follows.
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 register (see
Figure 6). 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 000
address. Table 6 shows the channel selection. The internal reference
selection connects the input of the ADC to a band gap reference.
When this selection is made and a conversion is initiated, the ADC
output must be approximately midscale. After power-up, the
default channel selection is DB2 = DB1 = DB0 = 0 (temperature
sensor).
Table 6. Channel Selection
DB2 DB1 DB0 Channel Selection Device
0 0 0 Temperature sensor All
0 0 1 Channel 1 All
0 1 0 Channel 2 AD7817
0 1 1 Channel 3 AD7817
1 0 0 Channel 4 AD7817
1 1 1 Internal reference (1.23 V) All
Overtemperature Register
If any of the five MSBs of the control byte are logic one, the entire
eight bits of the control byte are transferred to the overtemperature
register (see Figure 6). At the end of a temperature conversion,
a digital comparison is carried out between the 8 MSBs of the
temperature conversion result (10 bits) and the contents of the
overtemperature register (8 bits). If the result of the temperature
conversion is greater than the contents of the overtemperature
register (OTR), the overtemperature 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 7). However, the usable temperature range of
the temperature sensor is −55°C to +125°C. Figure 7 shows the
OTR and how to set TALARM (the temperature at which the OTI
goes low).
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, OTI goes 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.
DB2 DB1 DB0 ADDRESS REGISTER
LSBMSB
DB0 CONTROL BYTEDB7 DB6 DB5 DB4 DB3 DB2 DB1
DB0 OVERTEMPERATURE
REGISTER (OTR)
DB7 DB6 DB5 DB4 DB3 DB2 DB1
IF ANY BIT DB7 TO DB3 ARE LOGIC 0
THEN DB2 TO DB0 ARE WRITTEN TO
THE ADDRESS REGISTER
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
OVERTEMPERATURE REGISTER
01316-011
Figure 6. Address and Overtemperature Register Selection
DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
00001000
11111111
MINIMUM TEMPERATURE = –95°C
MAXIMUM TEMPERATURE = +152°C
MSB LSB
OVERTEMPERATURE REGISTER
OVERTEMPERATURE REGISTER (DEC) = T
ALARM
+ 103°C
T
ALARM
RESOLUTION = 18/LSB
01316-012
Figure 7. The Overtemperature Register (OTR)
AD7817/AD7818 Data Sheet
Rev. E | Page 12 of 20
CIRCUIT INFORMATION
The AD7817/AD7818 are single- and four-channel, 9 µs
conversion time, 10-bit ADCs with an on-chip temperature
sensor, reference, and serial interface logic functions on a single
chip. The ADC section consists of a conventional, successive
approximation converter based around a capacitor DAC. The
AD7817/AD7818 are capable of running on a 2.7 V to 5.5 V power
supply, and they 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 AD7817/AD7818 require a 2.5 V reference, which can be
provided from their internal reference or from an external
reference source. The on-chip reference is selected by connecting
the REFIN pin to analog ground.
CONVERTER DETAILS
Conversion is initiated by pulsing the CONVST input. The
conversion clock for the device is internally generated; therefore,
an external clock is not required, except when reading from and
writing to the serial port. The on-chip, track-and-hold goes from
track mode 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. A microcontroller
can use this signal to determine when the result of the conversion is
to be read. The track-and-hold acquisition time of the AD7817/
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 µs to complete. Temperature
measurement is explained in the Temperature Measurement
section.
The on-chip reference is not available, however, 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 Temperature Measurement Error Due to Reference Error
section.
Tie all unused analog inputs to a voltage within the nominal
analog input range to avoid noise pickup. For minimum power
consumption, tie the unused analog inputs to AGND.
TYPICAL CONNECTION DIAGRAM
Figure 8 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 the AD7817
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, connect a 10 µF capacitor between REFIN and AGND.
For applications where power consumption is a concern, use the
automatic power-down at the end of a conversion to improve
power performance. See the Power vs. Throughput section.
A
IN1
CONVST
AGND
DGND
REF
IN
V
DD
0.1µF10µF
D
OUT
RD/WR
A
IN2
A
IN3
A
IN4
D
IN
BUSY
OTI
SCLK
3-WIRE
SERIAL
INTERFACE
CS
AD7817
MICROCONVERTER/
MICROPROCESSOR
SUPPLY
2.7V TO 5.5V
OPTIONAL
EXTERNAL
REFERENCE
AD780/
REF-192
0V TO 2.5V
INPUT
10µF
EXTERNAL
REFERENCE
01316-013
Figure 8. Typical Connection Diagram
ANALOG INPUTS
Analog Input
Figure 9 shows an equivalent circuit of the analog input structure of
the AD7817/AD7818. The two diodes, D1 and D2, provide ESD
protection for the analog inputs. Take care to ensure that the
analog input signal never exceeds the supply rails by more than
200 mV. This causes these diodes to become forward-biased
and start conducting current into the substrate. The maximum
current these diodes can conduct without causing irreversible
damage to the device is 20 mA. The C2 capacitor in Figure 9 is
typically about 4 pF and can mostly be attributed to pin
capacitance. The R1 resistor is a lumped component made up
of the on resistance of a multiplexer and a switch. This resistor
is typically about 1 k. The C1 capacitor is the ADC sampling
capacitor and has a capacitance of 3 pF.
A
IN
D1 C1
3pF
V
DD
D2
C2
4pF
V
BALANCE
CONVERT PHASE—SWITCH OPEN
TRACK PHASE—SWITCH CLOSED
R1
1kΩ
01316-014
Figure 9. Equivalent Analog Input Circuit
Data Sheet AD7817/AD7818
Rev. E | Page 13 of 20
DC Acquisition Time
The ADC starts a new acquisition phase at the end of a conversion
and ends on the falling edge of the CONVST signal. At the end
of a conversion, a settling time is associated with the sampling
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
approximately 100 ns.
Figure 10 shows the equivalent charging circuit for the sampling
capacitor when the ADC is in its acquisition phase. R2 represents
the source impedance of a buffer amplifier or resistive network,
R1 is an internal multiplexer resistance, and C1 is the sampling
capacitor.
VIN
C1
3pF
R1
1kΩ
R2
01316-015
Figure 10. 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 (TCHARGE) is given by
TCHARGE = 7.6 × (R2 + 1 kΩ) × 3 pF
For small values of source impedance, the settling time associated
with the sampling circuit (100 ns) is, in effect, the acquisition
time of the ADC. For example, with a source impedance (R2) of
10 , the charge time for the sampling capacitor is approximately
23 ns. The charge time becomes significant for source impedances
of 1 kΩ 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 cause the THD to
degrade at high throughput rates.
ON-CHIP REFERENCE
The AD7817/AD7818 have an on-chip, 1.2 V band gap reference
that is gained up to give an output of 2.5 V. By connecting the
REFIN pin to analog ground, the on-chip reference is selected.
This selection causes SW1 to open and the reference amplifier
to power up during a conversion (see Figure 11). Therefore, the
on-chip reference is not available externally. An external 2.5 V
reference can be connected to the REFIN pin, which has the
effect of shutting down the on-chip reference circuitry and
reducing IDD by approximately 0.25 mA.
1.2V
REF
IN
SW1
2.5V
EXTERNAL
REFERENCE
DETECT
BUFFER
1.2V
26kΩ
24kΩ
01316-016
Figure 11. On-Chip Reference
ADC TRANSFER FUNCTION
The output coding of the AD7817/AD7818 is straight binary. The
designed code transitions occur at successive integer LSB values
(that is, 1 LSB, 2 LSBs, and so on). The LSB size is = 2.5 V/1024 =
2.44 mV. The ideal transfer characteristic is shown in Figure 12.
ANALOG INPUT
0V
1LSB +2.5V × 1LSB
1LSB = 2.5/1024
2.44mV
ADC CODE
111...111
111...110
111...000
011...111
000...010
000...001
000...000
01316-017
Figure 12. ADC Transfer Function
AD7817/AD7818 Data Sheet
Rev. E | Page 14 of 20
TEMPERATURE MEASUREMENT
The on-chip temperature sensor can be accessed via multiplexer
Channel 0, that is, by writing 0 0 0 to the channel address register.
The temperature is also the power on default selection. The
transfer characteristic of the temperature sensor is shown in
Figure 13. The result of the 10-bit conversion on Channel 0
can be converted to degrees centigrade by the following:
TAMB = −103°C + (ADC Code/4)
–55°C
+125°C
912Dec192Dec
TEMPERATURE
ADC CODE
01316-018
Figure 13. Temperature Sensor Transfer Characteristics
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.
Table 7 shows some ADC codes for various temperatures.
Table 7. 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 AD7817/AD7818 are trimmed using a precision 2.5 V
reference to give the transfer function previously described. 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 × VREF] − 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 produces a
gain error. This means that the temperature measurement 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 is 2.2 LSBs (+0.5°C) and 16 LSBs (+4°C) at +125°C.
SELF-HEATING CONSIDERATIONS
The AD7817/AD7818 have an analog-to-digital conversion
function capable of a throughput rate of 100 kSPS. At this
throughput rate, the AD7817/AD7818 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 rises as a result
of this power dissipation. Figure 14 to Figure 16 show the self-
heating effect in a 16-lead SOIC. Figure 14 and Figure 15 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 14, 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 15 where the heater is switched off after 2 sec. Figure 16
shows the relative effects of self-heating in air, fluid, and
thermal contact with a large heat sink.
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
–0.05
0 102030405060
TEMPERATURE (°C)
TIME (Seconds)
2-LAYER PCB
4-LAYER PCB
01316-019
Figure 14. Self-Heating Effect 2-Layer and 4-Layer PCB with the Heater
(6 mW) Turned Off After 30 sec
4-LAYER PCB
2-LAYER PCB
0.25
0.20
0.15
0.10
0.05
0
–0.05
012345
TEMPERATURE (°C)
TIME (Seconds)
01316-020
Figure 15. Self-Heating Effect 2-Layer and 4-Layer PCB with the Heater
Switched Off After 2 sec
Data Sheet AD7817/AD7818
Rev. E | Page 15 of 20
Figure 16 represents 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 in 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.
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–0.1
0161412108642
TEMPERATURE (°C)
TIME (Seconds)
AIR
FLUID
HEAT SINK
01316-021
Figure 16. Self-Heating Effect in Air, Fluid, and Thermal Contact with a Heat Sink
OPERATING MODES
The AD7817/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, that is, before BUSY goes low
(see Figure 17). When operating in this mode, do not initiate a
new conversion until 100 ns after the end of a serial read operation.
This quiet time is to allow the track-and-hold to accurately acquire
the input signal after a serial read.
Mode 2
In this mode of operation, AD7817/AD7818 automatically power
down at the end of a conversion (see Figure 18). The CONVST is
brought low to initiate a conversion and is left logic low until after
the end of the conversion. At this point, that is, when BUSY goes
low, the devices 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 AD7817/AD7818 only
to carry out a conversion (see the Power VS. Throughput section).
In Figure 18, the CS line is applicable to the AD7817 only.
AD7817/AD7818 Data Sheet
Rev. E | Page 16 of 20
DB7 – DB0
DB7(DB9) – DB0
D
OUT
SCLK
BUSY
D
IN
OTI
t
1
t
2
t
3
t
17
t
15
t
16
CONVST
CS
RD/WR
01316-023
Figure 17. Mode 1 Operation
DB7 – DB0
DB7(DB9) – DB0
D
OUT
SCLK
BUSY
D
IN
OTI
CONVST
CS
RD/WR
tPOWER-UP t1
t3
t15
t16
01316-024
Figure 18. Mode 2 Operation
Data Sheet AD7817/AD7818
Rev. E | Page 17 of 20
POWER vs. THROUGHPUT
Superior power performance can be achieved by using the
automatic power-down (Mode 2) at the end of a conversion
(see the Operating Modes section).
BUSY
C
ONVST
t
POWER-UP
2µs
t
CONVERT
8µs
t
CYCLE
100µs @ 10kSPS
01316-025
Figure 19. Automatic Power-Down
Figure 19 shows how the automatic power-down is implemented to
achieve the optimum power performance from the AD7817 and
AD7818. The devices operate in Mode 2, and the duration of
CONVST pulse is set 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.
For example, if the AD7817 operates in continuous sampling
mode with a throughput rate of 10 kSPS, the power consumption
is calculated as follows. The power dissipation during normal
operation is 4.8 mW, VDD = 3 V. If the power-up time is 2 µs,
and the conversion time is 9 µs, the AD7817 can typically dissipate
4.8 mW 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 while powered up during each cycle is
(11/100) × (4.8 mW) = 528 µW typical. Power dissipated while
powered down during each cycle is (89/100) × (3 V × 2 µA) =
5.34 µW typ. Overall power dissipated is 528 µW + 5.34 µW =
533 µW.
10
1
0.1
0.01
08070605040302010
POWER (mW)
THROUGHPUT (kHz)
01316-026
Figure 20. Power vs. Throughput Rate
AD7817 SERIAL INTERFACE
The serial interface on the AD7817 is a 5-wire interface that has
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 AD7817 operates in 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 device, the RD/WR line is set logic high
(see Figure 21). The serial interface on the AD7817 is designed
to allow the device 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.
DB9 DB8 DB7 DB0
DB1
DB7 DB6 DB5 DB1 DB0
SCLK
D
IN
123 123 910
RD/W
R
CS
87
CONTROL BYTE
D
OUT
t
4
t
5
t
10
t
11
t
8
t
9
t
6
t
7
t
13
t
14a
t
14b
t
12
01316-027
Figure 21. AD7817 Serial Interface Timing Diagram
AD7817/AD7818 Data Sheet
Rev. E | Page 18 of 20
Read Operation
Figure 21 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 (except for the first falling SCLK edge)
and are valid on the rising edge. During a read operation, 10 bits of
data are transferred. However, a choice is available to only clock
eight bits if the full 10 bits of the conversion result are not required.
The serial data can be accessed in a number of bytes if 10 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 be 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. The readback process is a
destructive process, in that once data is read back, it is erased. A
conversion must be done again; otherwise, no data is read back.
Write Operation
Figure 21 also shows the control byte write operation to the
AD7817. The RD/WR input goes low to indicate to the device
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,
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, that is, RD/WR, SCLK, and
DIN/DOUT (see Figure 8).
AD7818 SERIAL INTERFACE MODE
The serial interface on the AD7818 is a 3-wire interface that has
read and write capabilities. Data is read from the output register
and the control byte is written to the AD7818 via the DIN/DOUT
line. The AD7818 operates in 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 AD7818. When data is being written to the AD7818, the
RD/WR line is set logic low, and when data is being read from
the AD7818 the line is set logic high (see Figure 22). The serial
interface on AD7818 is designed to allow the AD7818 to interface
with 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 22 shows the timing diagram for a serial read from the
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/DOUT 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, a choice is available to only clock eight bits if the full
10 bits of the conversion result are not required. The serial data
can be accessed in a number of bytes if 10 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/DOUT pin becomes a logic
input on the falling edge of RD/WR.
Write Operation
A control byte write operation to the AD7818 is also shown in
Figure 22. The RD/WR input goes low to indicate to the device that
a serial write is about to occur. The AD7818 control bytes are
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 successive write to the AD7818 the RD/WR pin must
be brought logic high and low again.
SCLK
D
IN/OUT
RD/WR
t
5
t
7
t
8
t
9
t
11
t
12
t
13
t
14a
t
6
123 12 3 910
87
CONTROL BYTE
DB9 DB8 DB7 DB0DB1
DB0DB1
DB7 DB6 DB5
01316-028
Figure 22. AD7818 Serial Interface Timing Diagram
Data Sheet AD7817/AD7818
Rev. E | Page 19 of 20
OUTLINE DIMENSIONS
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
COMPLIANT TO JEDEC STANDARDS MS-012-AA
012407-A
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
0.50 (0.0196)
0.25 (0.0099) 45°
8°
0°
1.75 (0.0688)
1.35 (0.0532)
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0040)
4
1
85
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2441)
5.80 (0.2284)
0.51 (0.0201)
0.31 (0.0122)
COPLANARITY
0.10
Figure 23. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
COMPLIANT TO JEDEC STANDARDS MS-012-AC
10.00 (0.3937)
9.80 (0.3858)
16 9
8
1
6.20 (0.2441)
5.80 (0.2283)
4.00 (0.1575)
3.80 (0.1496)
1.27 (0.0500)
BSC
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0039)
0.51 (0.0201)
0.31 (0.0122)
1.75 (0.0689)
1.35 (0.0531)
0.50 (0.0197)
0.25 (0.0098)
1.27 (0.0500)
0.40 (0.0157)
0.25 (0.0098)
0.17 (0.0067)
COPLANARITY
0.10
8°
0°
060606-A
45°
Figure 24. 16-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-16)
Dimensions shown in millimeters and (inches)
COMPLIANT TO JEDEC STANDARDS MO-187-AA
6°
0°
0.80
0.55
0.40
4
8
1
5
0.65 BSC
0.40
0.25
1.10 MAX
3.20
3.00
2.80
COPLANARITY
0.10
0.23
0.09
3.20
3.00
2.80
5.15
4.90
4.65
PIN 1
IDENTIFIER
15° MAX
0.95
0.85
0.75
0.15
0.05
10-07-2009-B
Figure 25.8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
AD7817/AD7818 Data Sheet
Rev. E | Page 20 of 20
16 9
81
PIN 1
SEATING
PLANE
8°
0°
4.50
4.40
4.30
6.40
BSC
5.10
5.00
4.90
0.65
BSC
0.15
0.05
1.20
MAX
0.20
0.09 0.75
0.60
0.45
0.30
0.19
COPLANARITY
0.10
COMPLIANT TO JEDEC STANDARDS MO-153-AB
Figure 26. 16-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-16)
Dimensions shown in millimeters
ORDERING GUIDE
Model1 Temperature Range Temperature Error at 25°C Package Description Package Option Branding
AD7817ARZ −40°C to +85°C ±2°C 16-Lead SOIC_N R-16
AD7817ARZ-REEL7 −40°C to +85°C ±2°C 16-Lead SOIC_N R-16
AD7817ARU −40°C to +85°C ±2°C 16-Lead TSSOP RU-16
AD7817ARU-REEL7 −40°C to +85°C ±2°C 16-Lead TSSOP RU-16
AD7817ARUZ −40°C to +85°C ±2°C 16-Lead TSSOP RU-16
AD7817ARUZ-REEL7 −40°C to +85°C ±2°C 16-Lead TSSOP RU-16
AD7817BRZ −40°C to +85°C ±2°C 16-Lead SOIC_N R-16
AD7817BRZ-REEL −40°C to +85°C ±2°C 16-Lead SOIC_N R-16
AD7817BRZ-REEL7 −40°C to +85°C ±2°C 16-Lead SOIC_N R-16
AD7817BRU −40°C to +85°C ±1°C 16-Lead TSSOP RU-16
AD7817BRU-REEL7 −40°C to +85°C ±1°C 16-Lead TSSOP RU-16
AD7817BRUZ −40°C to +85°C ±1°C 16-Lead TSSOP RU-16
AD7817BRUZ-REEL −40°C to +85°C ±1°C 16-Lead TSSOP RU-16
AD7817BRUZ-REEL7 −40°C to +85°C ±1°C 16-Lead TSSOP RU-16
AD7817SR −40°C to +85°C ±2°C 16-Lead SOIC_N R-16
AD7818ARZ-REEL7 −40°C to +85°C ±2°C 8-Lead SOIC_N R-8
AD7818ARM −40°C to +85°C ±2°C 8-Lead MSOP RM-8 C3A
AD7818ARMZ −40°C to +85°C ±2°C 8-Lead MSOP RM-8 T1P
AD7818ARMZ-REEL −40°C to +85°C ±2°C 8-Lead MSOP RM-8 T1P
AD7818ARMZ-REEL7 −40°C to +85°C ±2°C 8-Lead MSOP RM-8 T1P
1 Z = RoHS Compliant Part.
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D01316-0-11/15(E)
