Circuit Note

CN-0216

Circuits from the Lab™ reference circuits are engineered and

tested for quick and easysystemintegrationto helpsolve today’s

analog, mixed-signal, and RF design challenges. For more

informationand/orsupport,visitwww.analog.com/CN0216.

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

Rev. 0

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whatsoeverconnectedtotheuseofanyCircuitsfromtheLabcircuits. (Continuedonlastpage)

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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.

33Ω

+5.0V

+5.0V

R2 1

1.3kΩ

R3 1kΩ

R4 1kΩ

R1 1

1.3kΩ

RG

60.4Ω

C2 3.3µF

C1 3.3µF

100pF

REFIN(+)

VDD

DIN

DOUT/RDY

SCLK

CS

REFIN(–)

AIN(+)

AIN(–)

GND

1µF

0.1µF

10µF

1µF

1µF

10µF

100pF

C3

C4

C5

+5.0V

ADA4528-1

AD7791

SDP BOARD

AND

SUPPORT CIRCUITS

ADA4528-1

ADP3301-5.0

SENSE+

SENSE–

OUT–

10µF

IN

IN

SD

OUT

OUT

NR

ERR

GND

0.1µF

0.1µF

4.7µF

5.0V

OUT+

LOAD CELL:

TEDEA HUNTLEIGH

505H-0002-F070

33Ω

33Ω

33Ω

+5.0V

Figure 1. Weigh Scale System Using the AD7791 (Simplified Schematic, All Connections and Decoupling Not Shown)