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TPS53626: System can not start up dur to ALERT# is pulled low by TPS53626

chentsu chung
Mastermind 6180 points
Part Number: TPS53626

Hi Sir,

The project use 3 TPS53626 for +VNN, +VSRAM and +VCORE.

Now the output voltage of these three TPS53626 are normal, and report PGOOD as well, but system can not start up dur to ALERT# is pulled low by TPS53626.

Thank you.

  • 0
    TI__Expert 4060 points

    Hi Chentsu,

    Can you please link to the schematic directly in this thread or send it to me in a private message? Our network block file sharing sites like Google Drive. 

    Also, please look at the system with the Fusion GUI running and connected to see if any faults are being logged during startup.

    Thanks,

    Carmen

  • 0 in reply to chentsu chung
    TI__Expert 4060 points
    Hi Chenstu,

    On all three schematics I do not see a pull-up resistor on ALERT# but you only gave me one page. Can you check the other pages with that signal in the full schematic to make sure it's pulled up to 1.05V somewhere?

    Also, have you double checked your DCR sensing circuit to make sure the time constant is matched to the inductor? I've seen designs in the past shutdown at startup because of a mismatch between the DCR time constant and sense circuitry.

    If you have a start up waveform you could send me that would be helpful too.

    Thanks,

    Carmen
  • 0 in reply to Carmen Parisi
    TI__Expert 4060 points
    One more thing - is the resistor from VOUT to the current sense circuitry (R232 in the VNN schematic) really 10kΩ? Usually that resistor is a much smaller value, like 10Ω. All three schematics show the same value and that could be your root cause too.

    Carmen
  • 0 in reply to Carmen Parisi
    Mastermind 6180 points

    Hi Carmen,

    Thanks for your response, there's a pull-up resistor on ALERT# on other page.

    For the concern about 10KOhm, It's should be Rpar as pic below

    And here's the waveform of start up:

    CH1:VR_ON, CH2:+VNN, CH3:PGOOD

     0131.tek00000.tif

    CH1:VR_ON, CH2:+VNN, CH3:ALERT#

     tek00001.tif

     

    Please help to check if there any could cause ALERT# goes low but DC/DC is still work, thank you very much.

  • 0 in reply to chentsu chung
    TI__Expert 4060 points
    Hi Chentsu,

    I see what you're saying about the 10kΩ resistor, sorry about that. I misread the schematic.

    From your waveforms, everything looks okay other than ALERT# not being pulled high, although it's always low which shouldn't be the case. Some other things to try:

    1) What else is on the SVID bus? Could you isolate the TPS53626 so it's the only regulator on the bus and see if ALERT# still low all the time?
    2)What happens when you read the Status Registers before and after enabling the rail, does ALERT# ever go high? Does the 626 or another regulator report a fault?

    Thanks,

    Carmen