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TPS7A4701-EP: Oscillation on Output of 7A4701

Larry Varnado
Prodigy 130 points
Part Number: TPS7A4701-EP

Hi,

We're experencing excessive oscillation on the output of our TPS7A4701.   We've tried both Adjustable and AnyOut and the problem persists.  We've tried soldering the FB pin directly to pin 1 (Output) which reduces the amplitude of the oscillation somewhat but it still persists.

Thanks

  • 0
    TI__Expert 4420 points
    Hi Larry, at first glance, the only comment I have is that either you use the feedback resistors or the fixed VOUT options but not both at the same time. I am assuming this is case but please confirm. Is the LDO the only component in the board where you are measuring VOUT? For further comments, I would need to see a plot of VIN and VOUT in the same graph during startup and steady state.

    Thanks,

    JV
  • 0 in reply to Javier Valle
    Prodigy 130 points

    Hello Javier,

    Yes we've tried both feedback and fixed out (not at the same time) but it didn't help with that ripple.

    The FB and choke reduce the ripple from 100 mVpp down to 20 mVpp but i still think its excessive.

    Here's the output and input (active probe on output, passive AC coupled on input).

    Thanks

    Larry

  • 0 in reply to Larry Varnado
    TI__Expert 4420 points

    Hi Larry, could you please:

    1. Show me a startup plot showing VIN and VOUT. I want to make sure this oscillation is not due to a specific startup condition.

    2. Let me know whether there are other components on the board you are using or is it only the LDO?

    Thanks,

    JV

  • 0 in reply to Javier Valle
    Prodigy 130 points

    Hi Javier,

    There are several other components on the board, here's other LDOs that seems to be working OK.

    Thanks

    Larry

  • 0 in reply to Larry Varnado
    TI__Expert 4420 points

    Hi Larry, sorry for the late reply. It seems the other LDOs that are working fine are not the same part as the one with the oscillating issue correct? My intent to get a full scope shot of the input and output voltages is to see how the output is responding as VIN rises. Based on the scope shot you sent, it seems like VOUT was rising properly and then it started to oscillate but I cannot be sure unless I see the entire VIN and VOUT rise curves. Can you please send me those?

    Thanks,

    JV