It is important to note that the external gate resistor is only a portion of the total resistance in the gate path. The schematic below shows all of the different components of gate resistance. Rgext(on) and Rgext(off) in the schematic below are the external gate resistors.

SiC MOSFETs are capable of withstanding several microseconds of short circuit conditions (MOSFET gated on with minimal resistance or inductance to limit the rate of current rise) where the drain current rises very quickly. However, in order to prevent damage to the MOSFET, the fault condition must be detected and the MOSFET turned off quickly.  

Although SiC MOSFETs do not exhibit desaturation behavior like IGBTs, the voltage across the drain to source of the part will increase as the current increases. Therefore, a circuit very similar to an IGBT desat circuit can be used to detect the fault condition. The exact voltage levels and timing requirements are different for SiC MOSFETs. We have worked closely with our gate driver partners at Analog Devices, Silicon Labs, Texas Instruments, NXP, and Broadcom to develop robust short-circuit protection solutions.

A report for short-circuit testing with one our 1200V MOSFET's is available here.

• Minimize the loop inductance of gate drive circuit

• Use the shortest leads possible for through-hole devices to minimize parasitic inductance

• Avoid overlapping of gate and drain traces to minimize Cgd and cross talk in hard switching bridge circuits

• Minimize common source inductance to prevent slowing down gate drive and gate oscillation for 3-lead devices. This can be done by making a kelvin connection where the device terminal meets the board. The gate drive circuit should connect to the source lead separately from the power path, and the gate drive circuit should not overlap the power circuit. Packages with kelvin source connections for the gate drive make it easier to separate these circuits on the PCB, and also improves switching speed.  

• Use low inductance DC bus configurations. Using high quality film and/or ceramic capacitors placed as closely to the devices as possible will help to reduce ringing and voltage overshoot at turn-off. The DC bus should use overlapping pours in a PCB or laminated bus structures when working with modules.