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UCC28056: About UCC28056, UCC25630 and UCC24610 in PMP21098

Zhun Liu
Intellectual 290 points
Part Number: UCC28056
Other Parts Discussed in Thread: PMP21098, UCC256304, UCC24610

1.UCC28056 (PFC)  and UCC25630(LLC DC/DC) are used in the schematic of the design PMP21098.

Now my idea is that: first the supply voltage of UCC28056 becomes Hi, and then UCC256304 works.

But it seems that supply VCC of UCC28056 is provided by PIN12(RVCC) of UCC256304. So if UCC256304 does not work, there is no RVCC to make  UCC28056 works.

Did I make a mistake?
Could you help me to find where VCC of UCC28056 comes from?

2. Two UCC24610 is used in PMP21098. Can I  replace it with just one TI's IC which can drive two GATEs?

(I have tried to search but nothing found.)

Thank you.

  • 0
    TI__Mastermind 26735 points
    Hi Zhun,

    UCC256304 has a high voltage startup function by its HV pin. This charges up the VCC capacitor. Once the VCC voltage is above the UVLO threshold, UCC256304 will generate the RVCC voltage. RVCC is then used to power UCC28056 to turn on the PFC stage.

    In theory, you could replace the two UCC24610's with a synchronous rectifier IC capable of driving two MOSFET's. I would need to check if TI has a SR IC capable of this. Most of the SR IC's I see are only pair with 1 MOSFET.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Intellectual 290 points

    Your answer is so fast and helpful. Thank you very much.

    And there is another questions.
    Now I need to reduce the size of the electrolytic capacitor in UCC28056 circuit. In the usual case(20kHZ) I need about 100uF's electrolytic capacitor.
    But When Ton=5.09us, 100kHZ(usually more than 20kHZ is OK,people cannot hear the noise), and Vin(AC)=90V , 150W ,

    because 100kHZ is much faster than 20kHZ, so I think it just need a smaller electrolytic capacitor, for example 50uF or smaller.

    But I,m not sure. Could you tell me whether it is right or not?

  • 0 in reply to Zhun Liu
    TI__Mastermind 26735 points

    Hi Zhun,

    It depends on how much AC ripple you are willing to tolerate and also how much hold up time your design requires. I think a good place to start is the UCC28056 design calculator to get a recommendation for the bulk capacitance of the PFC stage.

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    TI__Mastermind 26735 points

    Hi Zhun,

    To follow up, I am not seeing any SR controllers capable of driving both FET's on the secondary side.

    Best Regards,
    Ben Lough