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UCC28780: UCC28780+GaN+UCC24612 SR MOS damage

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Replies: 5

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Part Number: UCC28780

I use the UCC28780+GaN in my 65W A+C project, (has two ports: type A+type C).

 I open the port A output when the C port has 20V output, then the SR MOS damage.

My RM8 transformer turns ratio is 6.5, SR MOS Vds is 150V,

Do you have any suggestions to avoid this damage? thx.

  • Jack

    Do you have a schematic of how this design is implemented? From what you describe it sounds like you have a 2 output design, but when you have a load step transient from full to no load on the port A output it causes the SR FET to be damaged. Please correct me if I am not correct.

    We recommend to measure the voltage across the SR FET during this event when the voltage is below 20V. If you see a significant spike that's close to the VDS limit than the SR FET is probably failing due to a voltage overstress. We recommend that you either increase the VDS rating of the SR FET you are using or increase the snubber you have across the SR FET to reduce the voltage overshoot.

    Our reference design TIDA-01622 is close to your specification. As you can see in the design, a 150V FET is used for the SR and it has an RC snubber with 22ohm and 220pF. Your design may need different size components since this design is a single USB Type C PD output, but these values are a good starting place.

    Best Regards,
    Eric
  • In reply to Eric Faraci:

    Hi Eric:

    thank for your reply, please check the SCH as attached, thx66W GaN.sch

  • In reply to Jack Deng:

    Jack

    Please make sure that the RC snubber across the SR FET (R36 and C32) is populated in your design. If they are and you are still seeing the failures please either reduce R36 resistance or increase C32 capacitance.

    Best Regards,
    Eric
  • In reply to Eric Faraci:

    Hello Eick:
    In the light load, I can find that the SR Mos Vpeak would exceed 150V on UCC28780EVM-002.
    please check the other e2e link as below, thx.
    e2e.ti.com/.../796548.
  • In reply to Jack Deng:

    Jack

    We will reply to your question in the other E2E thread that you have a link to in your message.

    Eric

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