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UCC256404: UCC256404

Stuart Linzer
Intellectual 260 points
Part Number: UCC256404

Hi All, 

Designing PFC/LLC power supply.   PFC stage controller is powered from RVCC output of LLC controller.  During startup when RVCC turns on voltage on BLK pin is below BLKstop threshold (PFC is just starting).

Is BLKstop ignored at this point?  As PFC starts up, the voltage will rise above BLKstart and the LLC will start switching.  Is this when BLKstop becomes active?

-Stuart

  • 0
    TI__Genius 16155 points

    Hi Stuart,

    You are correct. BLKstop will be active once the LLC controller starts switching. 

    BLKstop voltage is useful for setting hold up time that is when PFC is off.

    BLKstart and BLKstop properly sets the power on sequence for AC-DC converter. 

    Power on sequence:

    Usually, It is better to startup PFC and then LLC. Doing so, you are allowing a lower startup current stress. UCC25640x RVCC is designed for this purpose. Once AC input is provided and VCC reaches 26V level, RVCC voltage is generated to power up PFC controller for PFC to boost. Once PFC boost to a level above UCC25640x BLK setting, LLC DC-DC start to operate. For any reason, if the BLK voltage reaches below BLKstop, switching stops.

    Please let me know if you have any further questions. 

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Intellectual 260 points

    Hi Manikanta,  

    Thank you for the information.  Another question:

    UCC256404 data sheet Device Comparison Table.  UCC256404A lists BW OVP Mode - Latch.  Does this mean power needs to be cycled to recover from an OVP event?

    -Stuart

  • 0 in reply to Stuart Linzer
    TI__Genius 16155 points

    Yes. That's correct.

    Regards

    Manikanta P