To set the gain of the difference amplifier, the common-mode range and output swing of the OPA397 must be

considered. Equation 3 and Equation 4 depict the typical common-mode range and maximum output swing,

respectively, of the OPA397 given a 3.3-V supply.

(3)

(4)

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.

are 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.

8.2.3 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

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OPA397

SBOSA02 – AUGUST 2021

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