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UCC28704: Schematic review for startup fail issue.

David Park
Expert 6450 points
Part Number: UCC28704

Tool/software:

Hi,

Could you review the schematic for startup fail issue?

2821.Schematic.pdf

In the customer's board, tried to turn on and there is startup fail after 50~60ms as below.

Thanks.

  • 0
    TI__Mastermind 24365 points

    Hi David,

    Thank you for reaching out.

    Looks like the system is shutting down due to OCP/OVP.

    1. The snubber capacitor looks very high at 220nF. Upto 10nF should be ok. According adjust the clamp resistor between 50-200k should be ok depending on the Vds spike.

    2. Add a cap on the CS pin -upto 120pf. Probably it could be shutting down due to noise on CS pin.

    3. Maybe consider adding a 10k resistor across gate source of MOSFET.

    4. Also consider adding snubber across secondary diode - if there is spike on secondary diode to clean up the aux winding waveform from potentially triggering OVP.

    Regards,

    Harish