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TPS 54331 over current

mitch meiss
Prodigy 170 points

Hi

attached is my design. I am having a weird problem. When I have C11 and C35 populated I am getting a high current draw of about 200mA that is causing an audible clicking sound from my inductor and is causing it to go into a protection mode. This causes short spikes at regulated 5V output and then it falls back to zero. I assume this is a protection that is in place because of the high current draw.  When they are not there things are working great (including the protection circuit for over voltage) and I get 5.02V output.

My question is why would two filter caps ever cause this to happen??

Attached is my schematic

Thanks

  • 0
    TI__Guru**** 191445 points
    Does this occur only during start up? As you note 200uF capacitance requires an additional 300 mA of start up current to charge the output caps up to 5 V. You might try increasing the SS cap C5 to 22 nF. Another possibility is inrush current. Electrolytic capacitors appear as near short circuit when voltage is initially zero. You could try adding 10 or 20 ohm in series, just as an experiment. Also, how close are the two caps to the TPS65331 output? If they are close, you may need to adjust the compensation to account for them.

    Let me know if any of these fix your issue or not.
  • 0 in reply to JohnTucker
    Prodigy 170 points
    It happens all of the time whether I populate 1 of them for a total capacitance of 100uF or both of them with 200uF. The caps are closer to the ATmega328 input than they are the TPS output.

    Changing C5 to 24.6nF (all that I had available was three 8.2nF caps) and that did the trick. The regulated voltage dropped to 4.6V though. I'm assuming just a voltage divider change should get me back to 5V?

    Also for my own knowledge, can you explain why changing the value of C5 fixed the problem?

    Thanks