The power dissipation of the DRV880x is a function of the RMS motor current and the each output’s FET resistance (RDS(ON)).
For this example, the ambient temperature is 35°C, and the junction temperature reaches 65°C. At 65°C, the sum of RDS(ON) is about 1Ω. With an example motor current of 0.8A, the dissipated power in the form of heat will be 0.8 A2x 1 Ω = 0.64 W.
The temperature that the DRV880x reaches will depend on the thermal resistance to the air and PCB. It is important to solder the device PowerPAD to the PCB ground plane, with vias to the top and bottom board layers, to dissipate heat into the PCB and reduce the device temperature. In the example used here, the DRV880x had an effective thermal resistance RθJA of 47°C/W, and: