The maximum value of the current-sense resistor is calculated based on choice of gain, the value of the maximum current the be sensed (I_MAX), and the power-supply voltage (V_IN+). When operating at the maximum current, the output voltage must not exceed the positive output swing specification, V_SP. Under the given design parameters, Equation 4 calculates the maximum value for R_SENSE as 47.2 mΩ.

Equation 4.

For this design example, a value of 40.2 mΩ is selected because, while the 40.2 mΩ is less than the maximum value calculated, 40.2 mΩ is still large enough to give an adequate signal at the current-sense amplifier output. To reduce resistor power losses or to operate over a reduced output range, smaller value resistors can be used as the expense of dynamic range and low current accuracy.