Hard-Switching Dynamic Rds,on Characterization of a GaN FET with an Active GaN-Based Clamping Circuit

Dynamic on-resistance (dR
_ds,on
) is a characteristic of enhancement-mode GaN FETs that has seen tremendous improvement in recent years, but it still presents a challenge in converter loss modeling and design. Measurement of dR
_ds,on
typically requires a clamping circuit that measures vds during the FET's on-state, but blocks the higher voltage from the measurement system during its off-state. This work proposed a dR
_ds,on
test circuit that uses an actively controlled eGaN® FET as the clamping mechanism, enabling fast stabilization to capture R
_ds,on
within 50 ns after hard turn-on transients. The test circuit was implemented in a typical half-bridge board with 100 V eGaN FETs and experimentally verified in a double pulse test with a 20 A inductive load. A similar board with 100 V Si MOSFETs was also tested for comparison. In both cases, the measured R
_ds,on
was within the datasheet-specified R
_ds,on
range up to the full rated voltage.