Optimum gate resistance value

im_zg

Hi,

for my application (three-phase inverter) I am using six CRD-001 SiC MOSFET Isolated Gate Driver and six C2M0160120D Silicon Carbide Power MOSFETs.

On the driver card, only R2, R4 and R5 are populated with 20 Ohm, which gives 6.66 Ohm gate resistance. The CRD-001 document says: "R9-R15 and diode D2 can be populated to provide optimum turn-on and turn-off performance". How to determine the optimum gate resistance value and if I need a diode or not? Max. DC voltage is 700 V, max, current is 5 Arms line and switching frequency is 6 kHz.

In my application, I am having an issue with serial communication breaking down and the noise might be coming from MOSFET switching. Now trying to reduce.

Thank you in advance.

Julius_R

The best method for choosing your gate resistance is by performing a double pulse test. The double pulse test will allow you to pulse the MOSFETs a couple of times using a function generator and measure the resulting turn-on switching energy, turn-off switching energy, peak voltage overshoot, peak current, dv/dt, and di/dt. We have an application note that explains how to perform the test https://assets.wolfspeed.com/uploads/2020/12/CPWRAN09.pdf. The fixture referenced in the application note is no longer available for purchase, but the test procedure is explained in the document. 

If you are having EMI issues, I would first recommend taking a close look at your layout first. You want to keep your bus inductance to a minimum (overlapping DC bus planes on adjacent layers). You can certainly increase Rg which would slow down switching speed and reduce peak voltage overshoot, current peaks, and ringing). The tradeoff is increased switching energy.  The double pulse test allows you to measure the effects of different values of gate resistance and select one that meets your requirements.  As to whether or not you need to utilize a diode, this will be determined by whether or not you can find a single value of Rg that meets your requirements during both turn-on and turn-off.  If your testing shows that the optimal value of Rg during turn-on is different than the optimal value of Rg during turn-off, then you would need to utilize the diode so that Rg can be fine-tuned separately for turn-on and turn-off.