The output voltage is set by applying a voltage from an external reference at REF. The reference input is

connected to internal gain network. The external resistor network of RFB1 and RFB2, connected to OUT, FB

and REF pins, set up adjustable gain as explained in Adjustable Gain Set Using External Resistors. Output is

set accurately at the voltage provided by external reference as shown in Equation 1 when the resistor RFB2 is

connected to the same voltage as REF pin. The voltage at REF pin can range between supply Vs and GND. For

symmetric bidirectional current sensing REF is set at mid-supply which sets out at mid-supply as well.

VOUT=G× ISHUNT +VREF

(1)

6.4.1.1 Reference Pin Connections for Unidirectional Current Measurements

Unidirectional operation allows current measurements through a resistive shunt in one direction. For

unidirectional operation, connect the device reference pin to the negative rail (see the Ground Referenced

Output section) or positive rail, VS. The required differential input polarity depends on the output voltage setting.

The amplifier output moves away from the referenced rail proportional to the current passing through the internal

shunt resistor.

6.4.1.2 Ground Referenced Output

When using the INA791x in unidirectional mode with a ground-referenced output, both REF input and resistor

RFB2 are connected to ground. Figure 6-5 shows how this configuration takes the output to ground when there is

0A flowing across the internal shunt.

OUT

FB

REF

VS

GND

2.7V to 5.5V

+

–

Alert

Rpullup

RFB1

RFB2

+

–

0.1 F

Shunt

Resistor

IS+

IS-

Shunt Current

LOAD

GND

IN-

IN+

Figure 6-5. Ground-Referenced Output

6.4.1.3 Reference Pin Connections for Bidirectional Current Measurements

Bidirectional operation allows the INA791x to measure currents through a resistive shunt in two directions. For

this case, set the output voltage anywhere within the reference input limits. A common configuration is to set the

reference inputs at half-scale for equal range in both directions. However, the reference input can be set to a

voltage other than half-scale when the bidirectional current is not symmetrical.

6.4.1.4 Output Set to Mid-Supply Voltage

Figure 6-6 shows two equal resistors R1 and R2 connected between VS and the GND pins divide the supply

at half, and by connecting REF pin to the divided supply, output is set to mid-supply voltage. The mid-point of

these resistors is buffered using external operational amplifier to avoid loading of resistors resulting in error. The

output is set to middle of the supply when there is no differential input voltage or 0A current in shunt resistor.

This method creates a ratiometric offset to the supply voltage, where the output voltage remains at VS / 2 when

0A of current flows through internal shunt resistor.

INA791A, INA791B

SBOSAD1A – MAY 2024 – REVISED JULY 2025

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