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UCC25600: schematic review

Dexter Choi
Expert 2795 points
Part Number: UCC25600

Dear Sir,

if it remove R9822 on the attached circuit. there are any side effect?

Vout: 68V

Iout: 2.6A

  • 0
    TI__Mastermind 27145 points

    Hi Dexter,

    R9822 appears to be a weak pullup on the OC pin to VCC of the LLC controller. Removing R9822 may have some effect on your overcurrent protection trip point.

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    Expert 2795 points

    Dear Ben,

    Thank you for your reply.

    My customer is saving BOM cost so They consider to remove R9822.

    could you explain more detail.

    We have tested it withoutR9822. OC point is same but when OC it hear audible noise at line filter. and OC release point is down more than before removing R9822.

    R9822 must be use or not.

    Thanks.

  • 0 in reply to Dexter Choi
    TI__Mastermind 27145 points

    Hi Dexter,

    RM9822 is not explicitly needed for the UCC25600 overcurrent protection to function properly. There are many reference design examples on ti.com using this controller that do not contain the weak pullup resistor between VCC and OC pins. 

    Without the pullup resistor, I would imagine the OC pin voltage discharges a bit faster so you might be seeing the frequency at which the controller attempts to restart, hits the OC fault, waits for OC to discharge to 0.6V and soft start again is slightly higher and in the audible frequency range. I would suggest trying a slightly larger filter capacitance on CM9808 and CM9809 to see if this can help avoid the audible noise. 

     Best Regards,

    Ben Lough