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TPS65130 +-15V with -15V slow oscillation

k1mgy
Expert 1680 points
Other Parts Discussed in Thread: TPS65130

My design is based on the reference (TPS65130 page 11, with specific changes for +-15V listed on page 12).  Layout is consistent with TI guidelines for this part.

Note that I had to combine the feedback resistors to achieve the proper values.

Building two identical boards I see the same strange issue on the -15V side (+15 regulates perfectly).  Here's a scope shot of the issue, viewed at OUTN:

Very slow oscillation.  At the moment, I'm befuddled.

Any ideas from TI or others?

  • 0
    TI__Expert 8010 points
    Hello K1mgy,

    Would you as well send me a scope plot showing the CN/CP- pin behavior? And what about the load? Are you seeing this problem with a load or in open loop?

    Thank you,
    Regards,
    ilona
  • 0 in reply to Ilona
    Expert 1680 points
    iLona, thank you for the ideas.

    So far I have constructed three boards using the same circuit. From each, I now get a different behaviour from the -15V side! The +15V stays in regulation nicely. I am unable to get a consistent result, therefore can't send you a scope trace yet. I very much suspect the board fabrication is crap. The house I am using has been mostly reliable, but as their boards are cheap, lately we have received poor quality.

    One note: with no loads on either rail all the boards draw almost 50ma from my +5V supply. This seems odd. I would expect the output capacitors to charge and then have the inductor current settle down. I am thinking this is a pointer to the trouble.. again the boards.

    I'm going to order TI's sample board and see how it behaves. If we have the same current draw with no load and a noisy -15V, then we can't use this device.
  • 0 in reply to k1mgy
    TI__Expert 8010 points
    Hello K1mgy,

    What happened on this request? Did you ordered TI samples and could progress?
    Let me have your feedback,

    Thanks,
    Ilona