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UCC2897A: we want to double check some items about UCC2897A

Frank Xiao
Genius 12055 points
Part Number: UCC2897A

Hi Team,

we want to double check some items about UCC2897A below.

1. whether we have formula for LINEOV resistor setting? Could you please share? We cannot find at the datasheet.

2. We want to check why we use the RC here. R18, C22 for the reference design.

3. do we have some methods to do primary soft start ?

Thanks.

  • 0
    TI__Expert 7080 points

    Hi Frank,

    Please see my reply in below:

    1. LINEOV pin is an input pin of internal comparator. the threshold of this comparator is 1.27V . that means once the voltage on LINEOV pin exceed 1.27V. it will trigger Line OVP. so 1.27V can be used for calculating output resistors, once you chose a down side resistor and the OVP point , you can calculate the up side resistor.

    2. R18 , C22, are loop compensation components , R18 series R20 and C22 configure as a zero , R18 and C22 configure as a pole. you can adjust there components to compensation the loop.

    3. I am sorry that I am a little confused by "Primary soft start" you descripted. Actually we already have a soft start pin "SS",  the circuit you shown on right side in my understanding is decrease the slew rate of Vout during soft start , if that is you wanted , I believe it maybe works.

    Hope can help you.

    Thanks.