when the REF pin is connected to ground. The output voltage in this configuration only responds to currents

that develop negative differential input voltage relative to the device IN– pin. Under these conditions, when

the negative differential input signal increases, the output voltage moves downward from the saturated supply

voltage. The voltage applied to the REF pin must not exceed VS.

Another use for the REF pin in unidirectional operation is to level shift the output voltage. Figure 7-5 shows an

application where the device ground is set to a negative voltage so currents biased to negative supplies, as seen

in optical networking cards, can be measured. The GND of the INA2191 can be set to negative voltages, as

long as the inputs do not violate the common-mode range specification and the voltage difference between VS

and GND does not exceed 5.5 V. In this example, the output of the INA2191 is fed into a positive-biased ADC.

By grounding the REF pin, the voltages at the output will be positive and not damage the ADC. To make sure

the output voltage never goes negative, the supply sequencing must be the positive supply first, followed by the

negative supply.

+ 1.8 V

IN-

IN+

VS

OUT

+

±

-3.3 V

RSENSE

Capacitively

Coupled

Amplifier

ENABLE

INA2191 (½)

REF

GND

- 3.3 V

ADC

CBYPASS

0.1 µF

Load

Figure 7-5. Using the REF Pin to Level-Shift Output Voltage

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INA191, INA2191

SLYS020C – FEBRUARY 2019 – REVISED AUGUST 2021

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