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UCC2897A: SS pin Capacitance value selection issue

BillTest BillTestAccount
Prodigy 60 points
Part Number: UCC2897A
Other Parts Discussed in Thread: TIDA-00539,

Dear Sir,

Our customer use UCC2897A follow TIDA-00539 schematic but Boot up some time will Failed. Measure OUT, SS and VDD pin waveforms as below (SS pin Capacitance value same is 10nF). Had change SS pin Capacitance to  22nF still can't Boot up. Could you let me know why the Boot up time is difference and some time Failed?  How to select SS pin cap. value? Thanks!

TPS2378 TIDA-00539 Schematic tidrez0.pdf

  • 0
    TI__Mastermind 27105 points
    Hi Sam.

    Thanks for your interest in UCC2897A. Could you share a startup waveform including the input voltge to the active clamp forward converter? Also could you tell me about the test conditions for these waveforms? Is this startup into no load? Typically the soft start capacitance is chosen using equations 13 and 14 of the UCC2897A datasheet: www.ti.com/.../ucc2897a.pdf.

    Best Regards,
    Ben Lough