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Low Power, 16-/24-Bit,
Sigma-Delta ADCs
AD7788/AD7789
FEATURES
AD7788: 16-bit resolution
AD7789: 24-bit resolution
Power
Supply: 2.5 V to 5.25 V operation
Normal: 75 μA maximum
Power-down: 1 μA maximum
RMS noise: 1.5 μV
AD7788: 16-bit p-p resolution
AD7789: 19-bit p-p resolution (21.5 bits effective)
Integral nonlinearity: 3.5 ppm typical
Simultaneous 50 Hz and 60 Hz rejection
Internal clock oscillator
V
DD
monitor channel
10-lead MSOP
FUNCTIONAL BLOCK DIAGRAM
REFIN(+) REFIN(–) GND
V
DD
AD7788/
AD7789
AIN(+)
AIN(–)
CLOCK
DOUT/RDY
DIN
SCLK
CS
03539-001
Σ-Δ
ADC*
SERIAL
INTERFACE
AND
CONTROL
LOGIC
*AD7788: 16-BIT ADC
AD7789: 24-BIT ADC
Figure 1.
GENERAL DESCRIPTION
The AD7788/AD7789 are low power, low noise, analog front
ends for low frequency measurement applications. The AD7789
contains a low noise, 24-bit, ∑-Δ ADC with one differential
input. The AD7788 is a 16-bit version of the AD7789.
The devices operate from an internal clock. Therefore, the
user does not have to supply a clock source to the devices.
The output data rate is 16.6 Hz, which gives simultaneous
50 Hz/60 Hz rejection.
The parts operate with a single power supply from 2.5 V to
5.25 V. When operating from a 3 V supply, the power dissi-
pation for the part is 225 μW maximum. The AD7788/AD7789
are available in a 10-lead MSOP.
INTERFACE
3-wire serial
SPI®-, QSPI™-, MICROWIRE™-, and DSP-compatible
Schmitt trigger on SCLK
APPLICATIONS
Smart transmitters
Battery applications
Portable instrumentation
Sensor measurement
Temperature measurement
Pressure measurement
Weigh scales
4 to 20 mA loops
Rev. B
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2006 Analog Devices, Inc. All rights reserved.
AD7788/AD7789
TABLE OF CONTENTS
Features .............................................................................................. 1
Interface ............................................................................................. 1
Applications....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
AD7789 .......................................................................................... 3
AD7788 .......................................................................................... 4
AD7788/AD7789.......................................................................... 5
Timing Characteristics ................................................................ 6
Timing Diagrams.......................................................................... 7
Absolute Maximum Ratings............................................................ 8
ESD Caution.................................................................................. 8
Pin Configuration and Function Descriptions............................. 9
Typical Performance Characteristics ........................................... 10
On-Chip Registers .......................................................................... 11
Communications Register......................................................... 11
Status Register............................................................................. 12
Mode Register ............................................................................. 13
Data Register............................................................................... 13
ADC Circuit Information.............................................................. 14
Noise Performance ..................................................................... 14
Digital Interface.......................................................................... 14
Circuit Description......................................................................... 17
Analog Input Channel ............................................................... 17
Bipolar/Unipolar Configuration .............................................. 17
Data Output Coding .................................................................. 17
Reference Input........................................................................... 17
V
DD
Monitor ................................................................................ 18
Grounding and Layout .............................................................. 18
Outline Dimensions ....................................................................... 19
Ordering Guide .......................................................................... 19
REVISION HISTORY
3/06—Rev. A to Rev. B
Changes to Ordering Guide .......................................................... 19
11/04—Rev. 0 to Rev. A
Updated Format..................................................................Universal
Added Footnote 2 to Integral Nonlinearity A Grade................... 4
Changes to Figure 5.......................................................................... 9
Updated Outline Dimensions ....................................................... 19
Changes to Ordering Guide .......................................................... 19
8/03—Revision 0: Initial Version
Rev. B | Page 2 of 20
AD7788/AD7789
SPECIFICATIONS
AD7789
V
DD
= 2.5 V to 5.25 V; REFIN(+) = 2.5 V; REFIN(−) = GND; GND = 0 V; all specifications T
MIN
to T
MAX
, unless otherwise noted.
Table 1.
Parameter
1
ADC CHANNEL SPECIFICATION
Output Update Rate
ADC CHANNEL
No Missing Codes
2
Resolution
Output Noise
Integral Nonlinearity
Offset Error
Offset Error Drift vs. Temperature
Full-Scale Error
3
Gain Drift vs. Temperature
Power Supply Rejection
ANALOG INPUTS
Differential Input Voltage Ranges
Absolute AIN Voltage Limits
2
Analog Input Current
Average Input Current
2
Average Input Current Drift
Normal-Mode Rejection
2
@ 50 Hz, 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz, 60 Hz
2
REFERENCE INPUT
REFIN Voltage
Reference Voltage Range
2
Absolute REFIN Voltage Limits
2
Average Reference Input Current
Average Reference Input Current Drift
Normal-Mode Rejection
2
@ 50 Hz, 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz, 60 Hz
1
2
AD7789B
16.6
24
19
1.5
±15
±3
±10
±10
±0.5
90
±REFIN
GND − 30 mV
V
DD
+ 30 mV
±400
±50
65
90
100
2.5
0.1
V
DD
GND − 30 mV
V
DD
+ 30 mV
0.5
±0.03
65
110
110
Unit
Hz nom
Bits min
Bits p-p
μV rms typ
ppm of FSR max
μV typ
nV/°C typ
μV typ
ppm/°C typ
dB min
V nom
V min
V max
nA/V typ
pA/V/°C typ
dB min
dB min
dB min
V nom
V min
V max
V min
V max
μA/V typ
nA/V/°C typ
dB min
dB typ
dB typ
Test Conditions/Comments
100 dB typ, AIN = 1 V
REFIN = REFIN(+) − REFIN(−)
Input current varies with input voltage
50 Hz ± 1 Hz, 60 Hz ± 1 Hz
AIN = 1 V
100 dB typ
50 Hz ± 1 Hz, 60 Hz ± 1 Hz
REFIN = REFIN(+) − REFIN(−)
50 Hz ± 1 Hz, 60 Hz ± 1 Hz
AIN = 1 V
50 Hz ± 1 Hz, 60 Hz ± 1 Hz
Temperature range:
−
40°C to +105°C.
Specification is not production tested but is supported by characterization data at initial product release.
3
Full-scale error applies to both positive and negative full scale and applies at the factory calibration conditions (V
DD
= 4 V).
Rev. B | Page 3 of 20
AD7788/AD7789
AD7788
V
DD
= 2.5 V to 5.25 V (B grade); V
DD
= 2.7 V to 5.25 V (A grade); REFIN(+) = 2.5 V; REFIN(−) = GND; GND = 0 V; all specifications
T
MIN
to T
MAX
, unless otherwise noted.
Table 2.
Parameter
1
ADC CHANNEL SPECIFICATION
Output Update Rate
ADC CHANNEL
No Missing Codes
2
Resolution
Output Noise
Integral Nonlinearity
Offset Error
Offset Error Drift vs. Temperature
Full-Scale Error
3
Gain Drift vs. Temperature
Power Supply Rejection
ANALOG INPUTS
Differential Input Voltage Ranges
Absolute AIN Voltage Limits
2
Analog Input Current
Average Input Current
2
Average Input Current Drift
Normal-Mode Rejection
2
@ 50 Hz, 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz, 60 Hz
2
REFERENCE INPUT
REFIN Voltage
Reference Voltage Range
2
Absolute REFIN Voltage Limits
2
Average Reference Input Current
Average Reference Input Current Drift
Normal-Mode Rejection
2
@ 50 Hz, 60 Hz
Common-Mode Rejection
@ DC
@ 50 Hz, 60 Hz
1
2
AD7788 A, AD7788B
16.6
16
16
1.5
±15
±50
±3
±10
±10
±0.5
90
90
±REFIN
GND − 30 mV
V
DD
+ 30 mV
Unit
Hz nom
Bits min
Bits p-p
μV rms typ
ppm of FSR max
ppm of FSR max
μV typ
nV/°C typ
μV typ
ppm/°C typ
dB min
dB typ
V nom
V min
V max
Test Conditions/Comments
B grade
A grade
2
B grade
A grade
REFIN = REFIN(+) − REFIN(−)
Input current varies with input
voltage
±400
±50
65
60
90
90
100
100
2.5
0.1
V
DD
GND − 30 mV
V
DD
+ 30 mV
0.5
±0.03
65
60
100
110
nA/V typ
pA/V/°C typ
dB min
dB min
dB min
dB typ
dB min
dB typ
V nom
V min
V max
V min
V max
μA/V typ
nA/V/°C typ
dB min
dB min
dB typ
dB typ
B grade, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
A grade, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
AIN = 1 V
B grade, 100 dB typ
A grade
B grade, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
A grade, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
REFIN = REFIN(+) − REFIN(−)
B grade, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
A grade
AIN = 1 V
50 Hz ± 1 Hz, 60 Hz ± 1 Hz
Temperature range: B grade:
−
40°C to +105°C; A grade:
−
40°C to +85°C.
Specification is not production tested but is supported by characterization data at initial product release.
3
Full-scale error applies to both positive and negative full scale and applies at the factory calibration conditions (V
DD
= 4 V).
Rev. B | Page 4 of 20
