The INAx181 are bidirectional, current-sense amplifiers capable of measuring currents through a resistive shunt in two directions. This bidirectional monitoring is common in applications that include charging and discharging operations where the current flowing through the resistor can change directions.
The ability to measure this current flowing in both directions is enabled by applying a voltage to the REF pin, as shown in Figure 45. The voltage applied to REF (VREF) sets the output state that corresponds to the zero-input level state. The output then responds by increasing above VREF for positive differential signals (relative to the IN– pin) and responds by decreasing below VREF for negative differential signals. This reference voltage applied to the REF pin can be set anywhere between 0 V to VS. For bidirectional applications, VREF is typically set at mid-scale for equal signal range in both current directions. In some cases, however, VREF is set at a voltage other than mid-scale when the bidirectional current and corresponding output signal do not need to be symmetrical.