The power dissipated by the sense resistor can be calculated from:

where

• P_D is the power dissipated by the resistor in Watts
• I_MAX is the maximum load current in A
• R_S is the sense resistor value in Ω.

The resistor must be rated for more than the expected maximum power (P_D), with margin for temperature derating. Be sure to observe any power derating curves provided by the resistor manufacturer.

Running the resistor at higher temperatures will also affect the accuracy. As the resistor heats up, the resistance generally goes up, which will cause a change in the measurement. The sense resistor should have as much heat-sinking as possible to remove this heat through the use of heatsinks or large copper areas coupled to the resistor pads. A reading drifting slightly after turnon can usually be traced back to sense resistor heating.