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TL431A-Q1: Weird Startup Behavior

Kevin Schmidgall
Expert 3870 points

Part Number: TL431A-Q1

Hello,

I have a customer seeing an overshoot of around 3.5V during startup with TL431-Q1 in configuration below:

Vo = 7.5V, Co = 20uF. The 2.5V feedback is being used in a comparator circuit so there is a 4.7uF cap on the feedback pin as well. Do you think this may have to do with all the capacitance on the feedback and output causing the output voltage control loop to slow down?

  • 0
    TI__Expert 3870 points

    So I know I just posted this but taking some time to throw some lines on the picture, it looks more like a regulation loop problem...When the output first hits 7.5V the feedback hasnt reached 2.5V. It doesnt reach 2.5V until the output hits that huge overshoot value.

  • 0 in reply to Kevin Schmidgall
    TI__Expert 3835 points
    Hi Kevin,

    I have emailed you privately and I believe we have resolved the issue. The customer has components on the FB pin which was causing the issue. The components should not be connect to the pin or have that large of a quantity.

    Let me know if you have any other questions.

    Thanks,
    Ethan