Current Sharing of Parallel SiC MOSFETs under Short Circuit Conditions

Device-to-device parametric variations (e.g. threshold voltage VTH, gate resistance RG and junction temperature TJ) can cause variations in the short-circuit currents conducted through parallel-connected devices. In this paper, the impact of variations in VTH, RG and TJ on current sharing under short-circuits is investigated using measurements and electrothermal modelling. The results show that VTH is the most critical parameter affecting short-circuit current sharing and directly impacts the peak short circuit current. Variations in gate resistance do not impact the short circuit current sharing unless the variation is over 400% thereby indicating catastrophic failure of the gate wirebond. Variation in the initial junction temperature is also not as critical as variations in VTH since the higher temperature device takes less short circuit current. Electrothermal simulations of parallel connected SiC MOSFETs have been developed to analyze how VTH mismatch impacts short circuit current sharing. These simulations allow for the investigation of the impact of VTH mismatch on the electrothermal stresses of the parallel connected MOSFETs.