INA4181A2 datasheet(20/62 Pages) TI2

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7.4 Device Functional Modes

7.4.1 Normal Mode

The INAx181 are in normal operation when the following conditions are met:

• The power supply voltage (VS) is between 2.7 V and 5.5 V.

• The common-mode voltage (VCM) is within the specified range of –0.2 V to +26 V.

• The maximum differential input signal times gain plus VREF is less than VS minus the output voltage swing to

VS.

• The minimum differential input signal times gain plus VREF is greater than the swing to GND (see the

Rail-to-Rail Output Swing section).

During normal operation, these devices produce an output voltage that is the gained-up representation of the

difference voltage from IN+ to IN– plus the reference voltage at VREF.

7.4.2 Unidirectional Mode

These devices can be configured to monitor current flowing in one direction (unidirectional) or in both directions

(bidirectional) depending on how the REF pin is configured. The most common case is unidirectional where the

output is set to ground when no current is flowing by connecting the REF pin to ground, as shown in Figure 7-6.

When the current flows from the bus supply to the load, the input signal across IN+ to IN– increases, and causes

the output voltage at the OUT pin to increase.

Power Supply, VS

2.7 V to 5.5 V

CBYPASS

0.1 µF

Single-Channel

TI Device

Bus Voltage

±0.2 V to +26 V

RSENSE

GND

Load

IN±

IN+

OUT

REF

Output

Figure 7-6. Unidirectional Application

The linear range of the output stage is limited by how close the output voltage can approach ground under

zero input conditions. In unidirectional applications where measuring very low input currents is desirable, bias

the REF pin to a convenient value above 50 mV to get the output into the linear range of the device. To limit

common-mode rejection errors, buffer the reference voltage connected to the REF pin.

A less-frequently used output biasing method is to connect the REF pin to the power-supply voltage, VS. This

method results in the output voltage saturating at 200 mV less than the supply voltage when no differential

input signal is present. This method is similar to the output saturated low condition with no input signal when

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

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

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

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

INA181, INA2181, INA4181

SBOS793H – APRIL 2017 – REVISED NOVEMBER 2023

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