The INA301-Q1 measures the differential voltage developed across a resistor when current flows through the component in order to determine if the current being monitored exceeds a defined limit. This resistor is commonly referred to as a current-sensing resistor or a current-shunt resistor, with each term commonly used interchangeably. The flexible design of this device allows for measuring a wide differential input signal range across the current-sensing resistor.

Selecting the value of this current-sensing resistor is primarily based on two factors: the required accuracy of the current measurement, and the allowable power dissipation across the current-sensing resistor. Larger voltages developed across this resistor allow for more accurate measurements to be made. Amplifiers have fixed internal errors that are largely dominated by the inherent input offset voltage. When the input signal decreases, these fixed internal amplifier errors become a larger portion of the measurement and increase the uncertainty in the measurement accuracy. When the input signal increases, the measurement uncertainty is reduced because the fixed errors are a smaller percentage of the signal being measured. Therefore, the use of larger-value, current-sensing resistors inherently improves measurement accuracy.

However, a system design trade-off must be evaluated through the use of larger input signals that improve measurement accuracy. Increasing the current sense resistor value results in an increase in power dissipation across the current-sensing resistor, and also increases the differential voltage developed across the resistor when current passes through the component. This increase in voltage across the resistor increases the power that the resistor must be able to dissipate. Decreasing the value of the current-shunt resistor reduces the power dissipation requirements of the resistor, but increases the measurement errors resulting from the decreased input signal. Selecting the optimal value for the shunt resistor requires factoring both the accuracy requirement for the specific application, and the allowable power dissipation of this component.

Low-ohmic-value resistors enable large currents to be accurately monitored with the INA301-Q1. An increasing number of very low-ohmic-value resistors are becoming more widely available, with values of 200 μΩ and less, and power dissipations of up to 5 W.