Dynamic hot spot temperature sensing in smart power switches

Thermal protection of Smart Power ICs in case of overload or short circuit requires a dynamic hot spot temperature measurement of the power switch. In most integrated Smart Power technologies however, the hot spot of the Power DMOS is not easily accessible by a sensor structure. This paper shows that the usual placement of the temperature sensor at the edge of the power switch leads to significant errors in absolute peak temperature measurement, but delivers satisfactory dynamic performance. It can thus be used for accurate thermal short circuit protection if the ratio of hot spot to sensor temperature rise is known. A thermal monitoring circuit is proposed that fully compensates for the error due to sensor placement and shuts down the power switch if either the hot spot or the sensor reaches a predetermined temperature limit.