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TPS53353: Questions for TPS53353 Output Voltage Drop from Light Load to Heavy Load

Part Number: TPS53353

Hi Experts,

Our customer is using our TPS53353 as the 12V to 1.2V power supply for their SoC Vcore, and found that it will see a output voltage drop when the load switched from light load to heavy load. We checked all the external circuits and actually the load is not very large, but no issues found related to this voltage drop. Can you kindly help to check what's possible reason for this issue? Thanks a lot!

Customer's application schematic is as below:

TPS53353 Schematic.pdf

Some waveform we captured for your reference:

Customer's PCB layout is as below:

  • Jacky,

    I have an idea what may be happening.  You have MODE pulled up to PGOOD with 100 k.  So when PGOOD is low, you will be in auto skip mode.  I suspect that the initial transient is enough to pull PGOOD low, causing TPS53353 to go int skip mode.  it take some milliseconds to exit skip mode.  During that time your output is collapsing.  Can you try connecting MODE to VREG temporarily to test?

    Best  Regards,

    John Tucker

    BSR-CCP LV/MV DC/DC Applications

  • In reply to JohnTucker:

    Hi John,

    Thanks for the comments, but we tried this method, it doesn't work. Finally we found that this issue is related to their poor decouple cap layout for the VREG pin, which the decouple cap is far away from the VREG pin with vias and will introduce the interference. Please see my explanation in below picture.

    After the PCB rework and put the decouple cap closed to the VREG pin, issue has been closed.

    Anyway, thanks for your suggestions for this issue.

    -Jacky

  • In reply to Jacky Wang(QD):

    Jacky,

    Yes poor PCB layout for VREG can certainly cause issues. Well noted!

    Best  Regards,

    John Tucker

    BSR-CCP LV/MV DC/DC Applications