# Mosfet Thermal Resistance calculation

I went through the application notes of infineon and TI. In the datasheet on the MOSFET, there is a junction to case Thermal Resistance given.

Can we use these values to calculate the power dissipation in the MOSFET? Since I read that the Thermal resistances given in the datasheet are measured assuming maximum temperature?

Pd= (Tj(max)-Ta)/(Rthjc-Rthca)(°C/W)

Tjmax=maximum junction temperature Ta=Ambient temperature Rthjc=Junction to case thermal resistance Rthca=Case to ambient thermal resistance (Heat Sink assumed?)

It is also said the cooling method used will be forced-air cooling which is bulky and not very easy to achieve. How do I calculate the heat sink parameter required for the temperature rise I calculate? Do I assume the value of Rthca (Heat Sink thermal resistance)? Is it possible to make a calculated assumption for the Rthca value?

Is it possible to know what extreme test conditions were used to measure the thermal resistances in the datasheet? How do they find these thermal resistance values Rthjc?

How will I be able to calculate the power dissipation due to thermal resistance? Do we assume a Junction temperature of approximately 110 degrees?

Is 25 degrees a good assumption for Ambient temperature or we use some standard temperature according to the application (40 degrees)?

also, how do we use Rthja (Junction-Ambient Thermal Resistance) in our calculation depending on the cooling area given in the datasheet?