7.3.5 Thermal Protection

Thermal protection disables the output when the junction temperature rises to approximately 160°C, allowing the device to cool. When the junction temperature cools to approximately 140°C, the output circuitry is again enabled. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal protection circuit may cycle on and off. This cycling limits the dissipation of the regulator, protecting it from damage due to overheating.

Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate heatsink. Junction temperature must be limited to 125°C maximum for reliable operation. To estimate the margin of safety in a complete design (including heatsink), increase the ambient temperature until the thermal protection is triggered; use worst-case loads and signal conditions. Thermal protection must trigger at least 35°C above the maximum expected ambient condition of your application for good reliability. This produces a worst-case junction temperature of 125°C at the highest expected ambient temperature and worst-case load.

The internal protection circuitry of the TPS737xx-Q1 is designed to protect against overload conditions. It was not intended to replace proper heatsinking. Continuously running the TPS737xx-Q1 into thermal shutdown degrades device reliability.