UCC21750: how to design the PNP for external CLMPI

YZ, 

If you have the option, I suggest to switch to a UCC217xx variant with external miller clamp pin (CLMPE), the performance is vastly superior to using PNP with internal miller clamp. 

Ye Zhao said:

Could you give me a design guide on how to choose the R1 and R2 as shown below in the illustration?

I prefer put R2/R1 as below. 

R2 should be >> R1 so that CLMPI does not sink the majority of current. 

R1, base resistor, should be sized according to your BJT current gain, I would choose it based on when VCE=2V and select according to the peak current you set (5A or larger is what i would target), since that is when the miller clamp turns on (VEE+2V)

You can also connect as follows if you wish. 

I would also suggest to run a simulation to confirm the operation in your system using the specific PNP spice model. 

Let me know if you have additional questions. 

Best

Dimitri

Yes that looks good. I would also suggest to test it with the UCC21750 spice model .

Best

Dimitri