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UCC256404: min and max resonant frequency limitation

Toshiro Imi
Expert 7190 points
Part Number: UCC256404

Hello,

Our customer has an question if UCC256404/403 has minimum and maximum resonant frequency limitation. As I checked  in the datasheet, I could not find. Please suggest him if UCC256404/403 has min, max resonant frequency and also let him know how to program.

Best regards,

  • 0
    TI__Mastermind 27105 points

    Hi Imi-san,

    UCC256404 is capable up to 1MHz switching frequency during startup and we typically recommend keeping the resonant frequency to 300kHz and below. The device can support down to 31.25kHz switching frequency based on the maximum allowable on time. No limit on minimum resonant frequency as long as the 31.25kHz min frequency number is ok for the power spec.

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    TI__Expert 7190 points

    Thank you very much for your suggestion. Can I make sure if UCC256404 build in frequency limit function. If it has not built-in, could you also let me know how UCC256404 works if the resonant frequency goes out of operation.

    Best regards,

  • 0 in reply to Toshiro Imi
    TI__Mastermind 27105 points

    Hi Imi-san,

    UCC256404 does not have a dfrequency limiting function but something we have done before is to place a resistor to gnd to always sink some current out of the FB pin as a way to limit the maximum FBreplica value and indirectly limit the minimum switching frequency.

    UCC256404 also has ZCS protection to avoid operating in the capacitive region. The controller is able to detect this and then ramp up the frequency to prevent capacitive region.

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    TI__Expert 7190 points

    Thank you very much for your help.

    I understand that UCC256404 has ZCS limitation for limiting the resonant frequency, that may be applied for low frequency region. A dummy load limits the higher side resonant frequency.

    Please correct me if my understanding is incorrect.

    Best regards,