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Original question:

TPS650864: Can't get Buck 1 working

TPS650864: LDO3P3 and LDO5 not work

ManKuen Kwok
Prodigy 10 points
Part Number: TPS650864

Hi, there
Recently we have designed a PCB using the TPS6508641 to power our MPSOC Zu3eg (Figure 1). We give a 12V supply to Vsys, but nothing come out, neither the LDOs nor the Bucks. So we
uninstall all the CSD87381 (U27/U28/U29) and 0 R(R305/R309/R334/R335/R317) , and just left Vsys , internal LDO3P3 and LDO5P0 there. But we found that even Vsys reach 12V, no output from the LDO3P3 and LDO5P0. It's weird because according to Datasheet, if Vsys > 5.6V , then these two LDOs will work anyway, no matter what CTL pins set.
We're kind of stuck there. Hope you can give any adivice , Thx!

  • 0
    TI__Mastermind 22295 points

    Hi ManKuen,

    You should see LDO5P0 and LDO3P3 ramp up once the VSYS voltage crosses the UVLO threshold of 5.6V.

    Can you share some scope captures of your power up waveforms?

    • Start with a capture of VSYS, LDO5P0, LDO3P3 in one picture. Please show the rising edge of all signals label the waveforms and time division
    • Next show LDO5P0, LDO3P3, CTL4, and BUCK1 output

    We can start with these and debug from there.

    Also, please share your schematic file as a PDF if possible so I can take a closer look.

    Regards,

    James