TIDT293 October 2022
Slow thermal failure occurs when the FET internal junction exceeds the FET rating without tripping temperature protection. This can occur when using a fan to cool the board. In this case, the temperature sensor remained cooled, while the MOSFET still heats internally. Generally, the FET (Q2) shorts and the sense resistor (R21) opens. Cooling the load step board with a fan is not recommended.