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Odd TPS54231 behaviour

Bernd Ocklin
Prodigy 90 points
Other Parts Discussed in Thread: TPS54231

I have issues with the TPS54231 in a new version of my boards. Hundreds of the previous version worked flawlessly.

What changed? As far as I can tell only the color of the silk screen from green to white! I would need some help for debugging, maybe a wrong cap somewhere?

I use the 5V design basically 100% as layed out in the datasheet, 12V in. Following some screen from the PH pin, overview and close-up. No load, should actually run in eco mode.

Thankful for any pointer or further investigation points,

Bernd

  • 0
    Prodigy 90 points

    One more thing: the result of the odd behavior is a 0V plus a couple of mV ripple at the output rather than the expected 3V3 (not 5V as I said above).

  • 0 in reply to Bernd Ocklin
    TI__Guru**** 191445 points

    Since you have a switching waveform I find it puzzling you have no output.  Perhaps the output is shorted?  Otherwise, you may need to replace each component in the circuit one by one with known good values.

  • 0 in reply to JohnTucker
    Prodigy 90 points

    Ha, thanks! I had replaced all components and checked for short circuits, but in this wrong order. I checked for shorts after component replacement.

    In fact none of the boards reflowed correctly, hot air rework remove the shortage under the 47uF caps. A 2nd reflow run with a slightly longer soak time fixed it for all other boards. This batch of PCBs must have different entities wrt reflow behavior.

    Bernd