The gain of the difference amplifier can now be calculated as shown in Equation 5.

Gain

=

Diff_Amp

V

V

= 15.5

V

V

R

(I

I

)

OUT_Max

OUT_Min

SHUNT

MAX

MIN

-

-

´

3.2 V

100 mV

100 m

-

W ´

- -

[1 A

( 1A)]

=

(5)

nearest standard value. Therefore, the ideal gain of the difference amplifier is 15.4 V/V.

were selected. This configuration reduces the likelihood that the design requires a two-point calibration. A simple

one-point calibration, if desired, removes the offset errors introduced by the 0.5% resistors.

8.2.1.3 Application Curve

1.65

-1.0

-0.5

0

0.5

1.0

0

3.30

Input Current (A)

Figure 8-2. Bidirectional Current-Sensing Circuit Performance: Output Voltage vs Input Current

8.2.2 Load Cell Measurement

Figure 8-3 shows the OPAx387 in a high-CMRR dual-op amp instrumentation amplifier with a trim resistor and

six-wire load cell for precision measurement.

GND

R

2

25 k

R

G

R

3

25 k

+

±

OPAx387

GND

5 V

R

4

100 k

REF5025

5 V

+

±

OPAx387

GND

5 V

R2

10 k

GND

V

OUT

R

4

100 k

5 V

G = 5 +

200 NŸ

R

G

+SENSE

±SENSE

Load Cell

Figure 8-3. Load Cell Measurement Schematic

OPA387, OPA2387, OPA4387

SBOS984F – NOVEMBER 2020 – REVISED FEBRUARY 2022

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