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TPS544C20: Turn on Waveform abnormality

Allen yang
Intellectual 910 points
Part Number: TPS544C20

Tool/software:

Hi Team,

TPS544C20 Abnormal voltage rise waveform during startup

  • 0
    TI__Guru 56925 points

     

    It a little hard to determine what is going on at 20ms/division, but I agree that it is not normal for the TPS544C20 to take 70ms to power up.

    One clear error in the schematic is PR131.  There should not be a connection between AGND and PGND external to the IC.  This can significantly impact the accuracy of current sense and may be triggering over-current protection despite low current due to the introduction of a ground loop.

    AGNDSNS is internally connected to PGND, and this should be the only connection between AGND and PGND.

    Additionally, It looks like there is not enough output capacitance to stablize the D-CAP2 control loop with C690015 (470pF from DIFFO to FB) in the feedback.

    I would recommend trying to remove PR131 and C690015 

  • 0 in reply to Peter James Miller
    Intellectual 910 points

    Hi Peter,

    This issue has not been improved after modification

    Are there any other methods?

    Thanks

  • 0 in reply to Allen yang
    TI__Guru 56925 points

    You removed both PR131 and C690015?

    Are you able to talk to the part via PMBus?  Knowing what status bits, if any, are being set would be very useful

    Can we zooom into the start-up?

    The soft-start time is suppose to be 2.7ms, so it would be good to look at the rise times to see if the part is starting up as intended, at about 1V/ms, or if it is being delayed some-how.

    Can we include VIN/VDD with the start-up?

    Zooming into the middle portion where the output is a saw-tooth at higher frequency would also be useful.