current sharing between parallel SiC MOSFETs

MiaoQ

Dear wolfspeed,

As we know, Si MOSFET has good charactor in current sharing between parallel MOSFET because Rdson will increase with Tj. But Vthgs of SiC MOSFET will decrease with Tj, so the SiC MOSFET with higher Tj will turn on firstly and turn off finally. Therefore, does the rising Tj grow the difference of current sharing between parallel SiC MOSFET?

YuequanHu

Thanks a lot for your questions on parallel switches.

Yes, you are right, as Tj increases, RDS_ON increases while Vth drops. As Vth drops the switch will turn on earlier and turn off later, which can cause switching loss increase. However, thanks to the RDS_ON positive temperature coefficient, the power loss and temperature increase will be limited due to higher RDS_ON thus lower shared current.

In order to have better thermal balance, we recommend placing the paralleled switches on the same heatsink so that they can balance each other’s temperature to offset the difference caused by different RDS_ON or Vth.

Hope this can answer your questions.