ADA4522-2ARMZ-R7 datasheet(39/48 Pages) AD

39 / 48 page

Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 39 of 48

Figure 83.Precision Weigh Scale Measurement System

Precision Low-Side Current Shunt Sensor

Many applications require the sensing of signals near the positive or negative rails. Current shunt sensors are one

such application and are mostly used for feedback control systems. They are also used in a variety of other

applications, including power metering, battery fuel gauging, and feedback controls in industrial applications. In

such applications, it is desirable to use a shunt with very low resistance to minimize series voltage drop. This

configuration not only minimizes wasted power, but also allows the measurement of high currents while saving

power.

A typical shunt may be 100 mΩ. At a measured current of 1 A, the voltage produced from the shunt is 100 mV, and the

amplifier error sources are not critical. However, at low measured current in the 1 mA range, the 100 µV generated

across the shunt demands a very low offset voltage and drift amplifier to maintain absolute accuracy. The unique

attributes of a zero drift amplifier provide a solution. Figure 84 shows a low-side current sensing circuit using the

ADA4522-1/ADA4522-2/ADA4522-4. The ADA4522-1/ADA4522-2/ADA4522-4 are configured as difference amplifiers

with a gain of 1000. Although the ADA4522-1/ADA4522-2/ADA4522-4 have high CMRR, the CMRR of the system is

limited by the external resistors. Therefore, as mentioned in the Single-Supply Instrumentation Amplifier section, the

key to high CMRR for the system is resistors that are well matched from both the resistive ratio and relative drift,

where R1/R2 = R3/R4.

Any unused channel of the ADA4522-1/ADA4522-2/ADA4522-4 must be configured in unity gain with the input

common-mode voltage tied to the midpoint of the power supplies.

Figure 84.Low-Side Current Sensing Circuit

OUT+

SENSE–

SENSE+

OUT–

VEXC

1/2

V+

R1 11.3kΩ

C1 3.3µF

1/2

ADA4522-2

R2 11.3kΩ

C2 3.3µF

60.4Ω

1kΩ

1µF

10µF

1µF

AIN(+)

REF(–)

REF(+)

DOUT/

RDY

DIN

AIN(–)

GND

VDD

+5V

AD7791

100pF

1µF

100pF

SCLK

LOAD

CELL

100kΩ

VSY

VOUT*

*VOUT = AMPLIFIER GAIN × VOLTAGE ACROSS RS

= 1000 × RS × I

= 100 × I

0.1Ω

100Ω

ADA4522-1/

ADA4522-2/

ADA4522-4

100kΩ

100Ω

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