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UCC28064A: SOFT START END OF UCC2806x IN "LED Driver Based on UCC28060 Interleaved ACDC Single Stage Flyback" Application (SLUA625)

Jiahui Jiang
Prodigy 40 points
Part Number: UCC28064A
Other Parts Discussed in Thread: PMP10116, UCC28060, UCC28063A,

Hello,

I have a question about UCC2806X in single stage flyback application.

I would like to know how the IC ends soft start in the application of SLUA625.

I think the VSENSE voltage can not reach nearly 96.5% of VSENSereg. How does it works?

Thank you.

  • 0
    TI__Genius 11350 points

    Hello Jiahui,

    Soft-start will be completed Vcomp reaches ~6V via charge current into C22.

    Ray

  • 0 in reply to Ray DiCecco
    Prodigy 40 points

    Hello，Ray，

    I may have confused the PMP10116 reference design with the SLUA625.

    One used UCC28060 and one used UCC28063A.

    UCC28060 ends soft start when Vcomp reaches ~ 6 V, UCC28063A when VSENSE reaches ~ 6 V.

    What I want to know is how the slow start in PMP10116 ends.

    I am going to use UCC28064A to make an application similar to PMP10116, but I have questions about this slow start.

    Because the voltage of the VSENSE in the PMP10116 does not exceed 5.1 V at most, because it is connected in parallel with a Zener diode.

    How does it end the soft start?

    Thank you.

    Jiahui

  • 0 in reply to Jiahui Jiang
    TI__Genius 11350 points

    Hi Jiahui,

    You are correct that the zener will interfere with the high gain mode of the soft-start as it will never reach 6V. In the PMP10116 design, they have essentially removed VSENSE from the feedback loop and replaced that with the output feedback through the optocoupler. The part will still soft-start and resume normal regulation based on the optocoupler/feedback signal regulating COMP directly. The one drawback of this design is that the COMP is always in the low gain mode which will reduce the loop response time.

    Regards,

    Ray