The thermally enhanced package provided with the DRV8332 is designed to interface directly to heat sink using a thermal interface compound in between, (that is, Ceramique from Arctic Silver, TIMTronics 413, and so on). The heat sink then absorbs heat from the ICs and couples it to the local air. It is also a good practice to connect the heatsink to system ground on the PCB board to reduce the ground noise.

R_θJA is a system thermal resistance from junction to ambient air. As such, it is a system parameter with the following components:

• R_θJC (the thermal resistance from junction to case, or in this example the power pad or heat slug)
• Thermal grease thermal resistance
• Heat sink thermal resistance

The thermal grease thermal resistance can be calculated from the exposed power pad or heat slug area and the thermal grease manufacturer's area thermal resistance (expressed in °C-in²/W or °C-mm²/W). The approximate exposed heat slug size is as follows:

• DRV8332, 36-pin PSOP3 …… 0.124 in² (80 mm²)

The thermal resistance of a thermal pad is considered higher than a thin thermal grease layer and is not recommended. Thermal tape has an even higher thermal resistance and should not be used at all. Heat sink thermal resistance is predicted by the heat sink vendor, modeled using a continuous flow dynamics (CFD) model, or measured.

Thus the system R_θJA = R_θJC + thermal grease resistance + heat sink resistance.

See the TI application report, IC Package Thermal Metrics (SPRA953), for more thermal information.