VOUT= VIN+−VIN− 1+2RFRG RG2RIN2 +VREF

(5)

This application uses the RES31A matched resistor chip from Texas Instruments. The resistors provide excellent

matching and temperature drift when compared to discrete 0.1% resistors. Resistor matching is critical to

achieving high common-mode rejection and low gain error. Figure 7-1 shows the final circuit. The circuit results

are shown in Figure 7-4, Figure 7-5. Note that the error is a simulated result at room temperature with typical dc

error values and worst case resistor matching values. Room temperature calibration is recommended to achieve

higher accuracy measurements.

To simplify this circuit further, the OPAx591 can be used to gain and buffer a readily available monolithic

difference amplifier, like INA132. The OPAx591 provide high gain and high input impedance necessary to

measure small current values.

+

–

V

IN

V

OUT

R

+

–

V

IN+

R

+

–

R

R

INA592

V+

V+

V++

OPAx591

V

REF

OPAx591

R

G

R

F

R

F

Figure 7-3. OPA591 Buffer for INA132

7.2.1.3 Application Curves

Input Current (

V)

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Figure 7-4. Output Voltage

Figure 7-5. Output Voltage and Error

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OPA591, OPA2591

SBOSA47A – FEBRUARY 2026 – REVISED SEPTEMBER 2026

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