New Dynamic Power MOSFET Model to Determine Maximum Device Operating Frequency

Improved SiC-MOSFETs with high HF-FOMs are enabling unprecedented high frequency MHz-switching. However, other SiC-MOSFET parameters, such as input capacitance and total gate resistance dictate the "theoretical limit" on the maximum switching frequency, and are often not considered. These latter parameters directly influence the "real-time" dynamic on-resistance when the propagation-time of gate voltage approaches that of the switching time period. To properly characterize MHz-switching performance, minimum switching times are calculated using a modified "input RC time constant" analysis that incorporates a time-dependent active area. An empirical comparison is conducted for several SiC-MOSFETs. A novel, equivalent RC ladder and resistor switch network model is proposed to describe the propagation of gate voltage and dynamic activation of unit-cells composing the SiC-MOSFET channel. A time-dependent effective on-resistance, accounting for transition and steady state conduction on-times, is determined and verified in both simulation and experiment. New high-frequency performance metrics for SiC-MOSFETs are proposed to provide greater insight for design engineers, and provide maximum expected operating limits. This will also help guide semiconductor designers to better match device to application.