SLIS175 November 2016 DRV8872-Q1
For optimal performance, the sense resistor must have the features that follow:
The power dissipated by the sense resistor equals IRMS2 × R. For example, if peak motor current is 3 A, RMS motor current is 1.5 A, and a 0.2-Ω sense resistor is used, the resistor dissipates 1.5 A2 × 0.2 Ω = 0.45 W. The power quickly increases with higher current levels.
Resistors typically have a rated power within some ambient temperature range, along with a derated power curve for high ambient temperatures. When a PCB is shared with other components generating heat, the system designer should add margin. It is always best to measure the actual sense resistor temperature in a final system.
Because power resistors are larger and more expensive than standard resistors, multiple standard resistors can be used in parallel, between the sense node and ground. This configuration distributes the current and heat dissipation.