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UCC28742: Are there soft start function?

Noriyuki Takahashi
Genius 10980 points
Part Number: UCC28742
Other Parts Discussed in Thread: TL431, UCC28780, UCC28740, UCC28610, LM5021, LM5023, UCC28600, TPS23752

Hi team,

Does this have soft-start function?

I guess this doesn't have, so could you tell which AC/DC controller devices have the function?

I would like to know it as a reference.

Regards,

Noriyuki Takahashi

  • 0
    TI__Mastermind 40520 points
    Hello Takahashi-san,

    The UCC28742 does not have built-in soft-start. Since the voltage-regulator part of the control loop is a TL431 type of shunt regulator on the secondary side, the soft-start function can be implemented there with a diode-connected capacitor on the cathode, and a pull-up resistor.

    Other secondary-side regulated devices similar to this include UCC28740, UCC28780, and UCC28610.

    AC-to-DC flyback controllers with built-in SS function include: LM5021, LM5023, and UCC28600.

    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    TI__Genius 10980 points
    Ulrich,

    Thanks.
    Could you show an example schematic of the soft-start function that can be implemented in the secondary side?
    It would be helpful if the example is used with UCC28742.


    Regards,
    Noriyuki Takahashi
  • 0 in reply to Noriyuki Takahashi
    TI__Mastermind 40520 points

    Hello Takahashi-san,

    I could not find an example of soft-start used specifically with the UCC28742, but I did find this reference involving the TPS23752:
    www.tij.co.jp/.../61-JAJSEO4E

    The soft-start circuit implementation for the TL431 shown here is identical for almost any other primary-side IC application, certainly including UCC28742.  I don't have design equations for the component value selections, but they can be determined partially by initial estimation and partially by trial and error.
     
    Regards,
    Ulrich