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TPS23754

Artem Tarabaev
Prodigy 10 points

HI
We have this schematic:

In the IC datasheet have point "8.2.2.15 Estimating Bias Supply Requirements and CVC". In this point estimating Cvc capacitors which equal 10uF. During Soft Start capacitor discharge to 8.5V and IC turn off. We increase capacity to 30 uF, but capacitors discharge at 2,5mS, but Soft Start execute 6ms at max load. We increase capacity to 130uF, and schematic worked. Why realy capacitor discharge faster than estimating?

  • 0
    TI__Expert 7500 points

    Hi Artem,

    I think your issue is Vc down to UVLO threshold. so your IC can't work.

    Below are my suggestion.

    1. FB resistor are 41.2K and 11.3K. Vout is only 11.6V.

        Vc will be lower than your expectation. 

    2.R1503 can reduce from 47-ohm to 10~20-ohm.

    3.Connect DT to VB. Disable GATE2 to reduce Vc loading.

    4.For the optocoupler ,U1502, the CTR of FOD817D is 300~600%. So R1517 should be 7.6K.

       I suggest you should change U1502 to FOD817A, CTR=80~160,and R1517 can be 2K-ohm.

    Regards,

    Ben

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