When performing a current measurement, the INA234 features very low input bias current which provides several benefits. The low input bias current of the INA234 reduces the current consumed by the device in both active and shutdown state. Another benefit of low bias current is that it allows the use of input filters to reject high-frequency noise before the signal is converted to digital data. In traditional digital current-sense monitors, the addition of input filters comes at the cost of reduced accuracy. However, as a result of the low bias current, the reduction in accuracy due to input filters is minimized. An additional benefit of low bias current is the ability to use a larger shunt resistor to accurately sense smaller currents. Use of a larger value for the shunt resistor allows the device to accurately monitor currents in the sub-mA range.

The bias current in the INA234 is the smallest when the sensed current is zero. As the current starts to increase, the differential voltage drop across the shunt resistor increases which results in an increase in the bias current (see Figure 6-14).

The INA234 has low bias current only when making a current measurement, when bus voltage measurements are made the impedance of the IN– will decrease. During bus voltage measurements the IN– pin will be connected to an internal resistor divider with an impedance of approximately 1 MΩ. Configuring the ADC to perform only current measurements will allow the device to always have low bias current.