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UCC25660: HV pin, soft start FB

Alain Zhu
Prodigy 10 points
Part Number: UCC25660

Tool/software:

UCC256603 HV

  1. In the case of “without HV startup” Can I let the HV pin OPEN? And apply a DC +16 V to the VCCP pin ?
  2. To realize very long term soft start, >> 25mS , can I add a clamper circuit to the FB pin. Let the clamping voltage rampup very slow, say 500mS , from 500mV~ 3.3V ?

Best

alainZ

  • 0
    TI__Genius 16155 points

    Hi Alainz,

    First of all please use UCU256613 instead of UCC256603 as we are going to NRND this part. 

    You can open HV pin or connect to GND in case of UCC2566x3. Apply VCCP more than VCC start threshold ~12V.

    To increase the soft start duration, you need to add soft start circuit on the secondary side of the LLC. 

    What's the current soft start duration that you are observing?

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Prodigy 10 points

    "...use UCU256613 instead of..." please send  me the specs of this chip.  I failed to find its specs.  

    my 2ndary side has huge bulk CAPs  +60V   4700uF x 5pcs, & -60V 4700uF x 5 pcs. 

    on the  primary side a flyback converter and MCU function good prior to the PFC/LLC startup. I want this MCU to control the FB pins  current to implement 500mS  LLC soft start.  what is  risk ?

    thanks

    alainz

     

  • 0 in reply to Alain Zhu
    TI__Genius 16155 points

    Hi Alain,

    You can find the datasheet of UCC25661x here:  UCC25661 data sheet, product information and support | TI.com

    You need to pull down the current from FB pin in order to control the switching frequency for this controller.

    So, you can not directly use the MCU to draw the current from FB pin. You will have to use an external circuit between the controller and MCU.

    Regards

    Manikanta P