SLVSEE8B November 2019 – May 2021 DRV8899-Q1
Figure 8-16 and Figure 8-17 show the variation of the RθJA (Junction-to-Ambient Thermal Resistance) and ΨJB (Junction-to-Board Characterization Parameter) with copper-pad area for 2-layer PCB, for the VQFN package. As shown in these curves, the thermal resistance is lower for the higher copper thickness PCB and the higher copper pad-area.
The thermal parameters (RθJA (Junction-to-Ambient Thermal Resistance) and ΨJB (Junction-to-Board Characterization Parameter)) are calculated considering the ambient temperature of 25°C and with 2-W power evenly dissipated between high-side and low-side FET's. The thermal parameters calculated considering the power dissipation at the actual location of the power-FETs rather than an averaged estimation.
The thermal parameters are highly dependent on the external conditions such as altitude, package geometry etc. Refer to Application Report for more details.