As we have previously discussed, this is likely due to runaway thermal behavior where your temperatures approach infinity. You must debug the underlying electrical and thermal circuit to ensure the conditions are appropriate for the device.
Some techniques to debug the thermal model:
- Ensure all electrical stresses are appropriate and within the device ratings. You cannot debug a thermal model if the electrical conditions will inherently lead to thermal runaway.
- You can fix the case temperature. If the temperature is still too high then the device is in appropriate for the conditions simulated in the model. If things look normal then it will also identify if the case-to-ambient thermal chain impedance is too large / inappropriate for the system requiring a refined design of the heatsink / cooling system.
- You can try having just one of your phases model thermally to minimize the combined contribution of all devices.
- Pick more appropriate devices or place more in parallel.
I’ll note you didn’t include your thermal model for the A4E120N50 device.