Hello Sahaja,

Thank you for reaching out. I believe I've identified the issue. In your calculation, it seems you considered only the thermal interface impedance (the MOSFET grease resistance, Rth,ch, which you set at 0.44 °C/W). This only accounts for the temperature difference between the heatsink and the case.

To accurately calculate the junction temperature, you also need to include the junction-to-case thermal impedance, which is approximately the same, at 0.44 °C/W for this device.

Using these values, the junction temperature can be calculated as follows:

• Rth junction to case (included in the device model) = 0.44 °C/W (approximately)
• Rth case to heatsink (MOSFET grease resistance Rth,ch) = 0.44 °C/W
• Power loss in the MOSFET = Switching loss + Conduction loss = 52.25 W
• Delta temperature = (0.44 + 0.44) * 52.25 = 45.98 °C
• Heatsink temperature (Heat sink model: Fixed) = 90 °C
• Junction temperature = Heatsink temperature + Delta temperature = 90 + 45.98 = 135.98 °C (approximately)

For more information on transient thermal impedance and its role in calculating junction temperature, please refer to our Application Note: "Introduction to Pulsed Current Safe Operating Area."

Let us know if you have any further questions!

Regards