CN0216 Datasheet, PDF (1/5 Pages) Analog Devices – Devices Connected

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Circuit Note
CN-0216
Devices Connected/Referenced
AD7791
Low Power, Buffered, 24-Bit Sigma-Delta
ADC
ADA4528-1
Precision, Ultralow Noise, Rail-to-Rail
Input/Output, Zero-Drift Op Amp
ADP3301
High Accuracy anyCAP® 100 mA Low
Dropout Linear Regulator
Precision Weigh Scale Design Using the AD7791 24-Bit Sigma-Delta ADC
with External ADA4528-1 Zero-Drift Amplifiers
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
CN-0216 Circuit Evaluation Board (EVAL-CN0216-SDPZ)
System Demonstration Platform (EVAL-SDP-CB1Z)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
CIRCUIT FUNCTION AND BENEFITS
The circuit in Figure 1 is a precision weigh scale signal
conditioning system. It uses the AD7791, a low power buffered
24-bit sigma-delta ADC along with two external ADA4528-1
zero-drift amplifiers. This solution allows for high dc gain with
a single supply.
Ultralow noise, low offset voltage, and low drift amplifiers are
used at the front end for amplification of the low-level signal
from the load cell. The circuit yields 15.3 bit noise-free code
resolution for a load cell with a full-scale output of 10 mV.
This circuit allows great flexibility in designing a custom low-
level signal conditioning front end that gives the user the ability
to easily optimize the overall transfer function of the combined
sensor-amplifier-converter circuit. The AD7791 maintains good
performance over the complete output data range, from 9.5 Hz
to 120 Hz, which allows it to be used in weigh scale applications
that operate at various low speeds.
+5.0V
+5.0V
0.1µF 10µF
ADA4528-1
+5.0V
LOAD CELL:
TEDEA HUNTLEIGH _SENSE+
505H-0002-F070
OUT–
OUT+
SENSE–
RG
60.4Ω
R1 11.3kΩ
C1 3.3µF
C2 3.3µF
R2 11.3kΩ
+5.0V
ADA4528-1
VDD
100pF
1µF
AD7791
REFIN(+)
REFIN(–)
SDP BOARD
AND
SUPPORT CIRCUITS
100pF
R3 1kΩ ^{1µF C3}
AIN(+)
10µF C5
AIN(–)
R4 1kΩ _{1µF C4}
DIN
33Ω
DOUT/RDY
33Ω
SCLK
33Ω
CS
33Ω
GND
V_IN
10µF 0.1µF
ADP3301-5.0
IN
OUT
IN
OUT
SD
NR
ERR
GND
5.0V
0.1µF 4.7µF
Figure 1. Weigh Scale System Using the AD7791 (Simplified Schematic, All Connections and Decoupling Not Shown)
Rev. 0
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