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UCC28782EVM-030: UCC28782

Rex Wu
Prodigy 10 points
Part Number: UCC28782EVM-030
Other Parts Discussed in Thread: UCC27712

Hello 

I have an issue when I change to use silicon (Si) power FETs on the primary side,

due to i would like to use silicon (Si) power FETs on the primary side,

I have reworked the SET pin connection (SET pin connect to Ref pin and make sure disconnect to AGND on EVM),

but it goes to DCM at 115Vac/20Vdc/3.25A, not BCM

could you help me to optimize to operating in BCM.

  • +1
    TI__Expert 7080 points

    Hi Rex,

    Could you share the schematic to me for reviewing , if it's confidential that can't public on this thread, please send a E-mail to me : jaden-ning@ti.com.

    May i ask which board you are testing when you change the GaN FET to Silicon FET , your own board or TI EVM board . for GaN FET with integrated driver , the high side driver on EVM board is a isolation driver without driver capability . but if change to silicion FET , what we need is a halfbridge driver . I am afraid the above waveform shown the controller is operating at BCM mode , but high side silicon FET didn't turn on .looks like it running at DCM mode . if high side don't turn on  . the controller can't detect a ZVS on low side due to there is no negative current. it will extend the PWMH until internal tuner saturation . what you can see from the waveform is a long PWMH pulse . so i guess your high side FET didn't responded to the PWMH .

    Thanks.

  • +1 in reply to Jaden Ning
    Prodigy 10 points

    Hello Jaden

    i use a small board with silicon fet, and then attach to TI EVM board, please refer the small board schematic as following.

  • +1 in reply to Rex Wu
    TI__Expert 7080 points

    Hi Rex,

    ISO7710FD is a isolator driver, can't be used to directly driver a silicon FET , you have to use a half-bridge driver such as UCC27712 to replace ISO7710FD.

    Thanks.

  • 0 in reply to Jaden Ning
    Prodigy 10 points

    thanks for your support.