This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC21750: how to design the PNP for external CLMPI

Part Number: UCC21750

hello TI support

Using the external CLMPI on UCC21750:

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

What would be other design considerations?

In my case, I have 3 x IGBTs in parallel with 3 individual BJT buffers and 3 individual PNP CLMPI.

Thanks a lot!

YZ

  • 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. 

    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

  • Dimitri

    Thanks a lot for your explanation. I did some LTspice simulation as follows, using the other circuit you just suggested.

    Does it look good to you?

    Thanks

    YZ

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

    Best

    Dimitri