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AD7796BRUZ

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24
Low Power, 16-/24-Bit Sigma-Delta ADC
for Bridge Sensors Low Power, 16-/24-Bit
Data Sheet
AD7796/AD7797
Rev. B Document Feedback
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 ©2006–2016 Analog Devices, Inc. All rights reserved.
Technical Support www.analog.com
FEATURES
RMS noise: 65 nV
Instrumentation amp
Temperature sensor
Internal clock oscillator
Simultaneous 50 Hz/60 Hz rejection
Update rate range: 4.17 Hz to 123 Hz
Current: 250 µA typ
Power-down: 1 µA
Power supply range: 2.7 V to 5.25 V
–40°C to +85°C temperature range
Independent interface power supply
16-lead TSSOP
INTERFACE
3-wire serial
SPI, QSPI™, MICROWIRE, and DSP compatible
Schmitt trigger on SCLK
APPLICATIONS
Weigh scales
Strain gages
Industrial process control
Instrumentation
Portable instrumentation
FUNCTIONAL BLOCK DIAGRAM
AD
7796/
AD
7797
DO
UT
/
RDY
D
I
N
S
C
L
K
AI
N
(+)
A
I
N
(
–
)
M
U
X
G
N
D
Σ
-Δ
AD
C
A
V
D
D
×
12
8
R
EF
E
R
E
NC
E
T
EMP
SEN
S
O
R
IN
T
ERNA
L
CL
O
CK
G
N
D
AV
D
D
R
E
F
I
N
(
–
)
R
E
F
I
N
(+)
C
L
K
AD
7796:
16-
B
IT
ADC
AD
7797
: 24
-
BI
T AD
C
SE
R
I
A
L
I
N
TE
RF
AC
E
AN
D
C
O
N
T
R
O
L
L
OGI
C
C
S
D
V
D
D
06083-001
Figure 1.
GENERAL DESCRIPTION
The AD7796/AD7797 are complete, analog front ends for high
precision, bridge sensor applications such as weigh scales. The
AD7796/AD7797 contain a Σ-∆ ADC capable of 16-/24-bit
resolution, respectively. The on-chip instrumentation amplifier
has a fixed gain of 128, allowing small amplitude signals such as
those from bridge sensors to be directly interfaced to the ADC.
Each device has one differential input and contains a temperature
sensor that is internally connected to the ADC. This sensor can
be used to perform temperature compensation of the bridge.
The devices can be operated with the internal clock or an external
clock. The output data rate from the devices is software-
programmable and can be varied from 4.17 Hz to 123 Hz.
The AD7796/AD7797 operate with a power supply from 2.7 V
to 5.25 V. Each device consumes a current of 250 µA typical and
is housed in a 16-lead TSSOP.
AD7796/AD7797 Data Sheet
Rev. B | Page 2 of 24
TABLE OF CONTENTS
Features .............................................................................................. 1
Interface ............................................................................................. 1
Applications ....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Timing Characteristics ..................................................................... 5
Timing Diagrams .......................................................................... 6
Absolute Maximum Ratings ............................................................ 7
Thermal Resistance ...................................................................... 7
ESD Caution .................................................................................. 7
Pin Configuration and Function Descriptions ............................. 8
RMS Noise and Resolution Specifications .................................... 9
Typical Performance Characteristics ........................................... 10
On-Chip Registers .......................................................................... 11
Communication Register .......................................................... 11
Status Register ............................................................................. 12
Mode Register ............................................................................. 12
Configuration Register .............................................................. 14
Data Register ............................................................................... 14
ID Register................................................................................... 14
Offset Register ............................................................................ 15
Full-Scale Register ...................................................................... 15
ADC Circuit Information .............................................................. 16
Overview ..................................................................................... 16
Digital Interface .......................................................................... 17
Circuit Description......................................................................... 20
Analog Input Channel ............................................................... 20
Bipolar/Unipolar Configuration .............................................. 20
Data Output Coding .................................................................. 20
Reference ..................................................................................... 20
Reset ............................................................................................. 21
Burnout Currents ....................................................................... 21
AV
DD
Monitor ............................................................................. 21
Temperature Monitor ................................................................ 21
Calibration ................................................................................... 21
Grounding and Layout .............................................................. 22
Applications Information .............................................................. 23
Weigh Scales ................................................................................ 23
Outline Dimensions ....................................................................... 24
Ordering Guide .......................................................................... 24
REVISION HISTORY
3/16—Rev. A to Rev. B
Changes to RS2, RS1, RS0 = 0, 0, 0; Power-On/Reset = 0x80
Section and Table 11 ....................................................................... 12
8/06—Rev. 0 to Rev. A
Changes to Table 1 ............................................................................ 3
Changes to Figure 5 .......................................................................... 8
Changes to Table 14 ........................................................................ 13
7/06—Revision 0: Initial Version
Data Sheet AD7796/AD7797
Rev. B | Page 3 of 24
SPECIFICATIONS
AV
DD
= 2.7 V to 5.25 V, DV
DD
= 2.7 V to 5.25 V, GND = 0 V, all specifications T
MIN
to T
MAX
, unless otherwise noted.
Table 1.
Parameter AD7796B/AD7797B
1
Unit Test Conditions/Comments
ADC CHANNEL
Output Update Rate 4.17 to 123 Hz nom
No Missing Codes
2
24 Bits min AD7797 only
16 Bits min AD7796 only
Resolution See Table 7 and Table 8
RMS Noise and Update Rates See Table 6
Integral Nonlinearity
±10
ppm of FSR typ
Offset Error
3, 4
±1 µV typ
Offset Error Drift vs. Temperature
4
±10 nV/°C typ
Full-Scale Error
3, 4, 5
±10 µV typ
Gain Drift vs. Temperature
4
±3 ppm/°C typ
Power Supply Rejection 90 dB min AIN = 1 V/128
ANALOG INPUTS
Differential Input Voltage Ranges ±V
REF
/128 V nom V
REF
= REFIN(+) – REFIN(–)
Absolute AIN Voltage Limits
2
GND + 300 mV V min
AV
DD
− 1.1 V max
Common-Mode Voltage, V
CM
0.5 V min V
CM
= (AIN(+) + AIN(–))/2
Analog Input Current
Average Input Current
2
±250 pA max Update rate < 100 Hz
Average Input Current Drift ±2 pA/°C typ
Normal Mode Rejection
2
Internal Clock
At 50 Hz, 60 Hz 65 dB min 80 dB typ, 50 ± 1 Hz, 60 ± 1 Hz, FS[3:0] = 1010
6
At 50 Hz 80 dB min 90 dB typ, 50 ± 1 Hz, FS[3:0] = 1001
6
At 60 Hz 90 dB min 100 dB typ, 60 ± 1 Hz, FS[3:0] = 1000
6
External Clock
At 50 Hz, 60 Hz
80
dB min
6
At 50 Hz 94 dB min 100 dB typ, 50 ± 1 Hz, FS[3:0] = 1001
6
At 60 Hz 90 dB min 100 dB typ, 60 ± 1 Hz, FS[3:0] = 1000
6
Common-Mode Rejection
At DC 90 dB min AIN = 7.81 mV
At 50 Hz, 60 Hz
2
90
dB min
At 50 Hz, 60 Hz
2
90 dB min
50 ± 1 Hz (FS[3:0] = 1001
6
), 60 ± 1 Hz,
FS[3:0] = 1000
6
REFERENCE
External REFIN Voltage 2.5 V nom REFIN = REFIN(+) – REFIN(–)
Reference Voltage Range
2
0.1 V min
AV
DD
V max
Absolute REFIN Voltage Limits
2
GND − 30 mV V min
AV
DD
+ 30 mV V max
Average Reference Input Current 400 nA/V typ
Average Reference Input Current Drift ±0.03 nA/V/°C typ
Normal Mode Rejection Same as for analog inputs
Common-Mode Rejection 100 dB typ
TEMPERATURE SENSOR
Accuracy ±2 °C typ Applies if user calibrates the temperature sensor
Sensitivity 0.81 mV/°C typ
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24

AD7796BRUZ

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Analog to Digital Converters - ADC Low Power 16-Bit
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