Statistical Analysis of the Electrothermal Imbalances of Mismatched Parallel SiC Power MOSFETs

Thanks to the increasing availability of silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) with outstanding static and dynamic performances, the number of applications in which these devices are used is rapidly growing. Despite that, the maximum current rating of such devices is usually limited at few hundred amps, which sets an upper bound for the power level at which these transistors can be adopted. A viable solution to this problem consists in paralleling several SiC MOSFETs. However, the design of parallel configurations needs optimization since mismatched performances can cause the enhanced stress of a subset of devices, which can ultimately lead to premature failure of the whole module. In this contribution, several sets of Monte Carlo (MC) electrothermal simulations of parallel SiC MOSFETs are used to systematically relate the deviations of devices and circuit parameters to the resulting uneven power dissipation. To this purpose, a set of relevant parameters is identified and statistically described. Thereafter, the simulation of a 200-kHz synchronous buck converter relying on mismatched parallel MOSFETs is performed as a case study. Eventually, a methodology to derive a guideline for the design of reliable multichip configurations is developed. The methodology is based on the iteration of MC simulations for different tolerances of the parameters.