Hello Kai,
I understand that you want to accurately model the thermal behaviour of a MOSFET mounted on a PCB that is smaller than the 1 sq. inch, as referenced by the manufacturer.
The heat dissipation from top side is generally a less significant path than the thermal pad dissipation, but it should not be disregarded as it can contribute to overall cooling, particularly with airflow or in cooler environments.
Your approach to calculate overall thermal resistance as a parallel circuit for the main paths is accurate, and calculating thermal capacitance similarly will provide a realistic transient thermal model.
The model is likely a “Cauer” thermal model, accounting for physical layout and heat flow through PCB layers.
You can use the CF1 value from the manufacturer's model as a starting point for the junction's thermal capacitance in your Simscape simulation.
To know more about “Cauer” thermal model and basic thermal blocks and modelling technique in Simscape, please refer to the following MATLAB documentations.
- Cauer thermal model: https://www.mathworks.com/help/sps/ref/cauerthermalmodel.html
- Basic thermal blocks and modelling techniques: https://www.mathworks.com/help/simscape/thermal-models.html
Hope this helps,
Regards,
Sankalp dev
