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PS_NVVDD_EN_R low - circuit question

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    PS_NVVDD_EN_R low - circuit question

    Hello,
    I have a possibly stupid question which I am, unfortunately, already trying to figure out for some time.

    I have a card (reference 1080Ti) that has PS_NVVDD_EN present (3v) while PS_NVVDD_EN_R is low. The schematics doesn't quite make sense to me as both of the resistors that are connecting PS_NVVDD_EN_R line to 1V8 and PS_NVVDD_EN are omitted (R536 and R535).

    And now the stupid part - which component is responsible for pulling the PS_NVVDD_EN_R line high?

    Thank you.

    #2
    Re: PS_NVVDD_EN_R low - circuit question

    Schematic in question - there's no other connection except those two mosfets. Is there a way the rail is getting powered from EN_Q through them?

    My understanding is that once PS_NVVDD_EN is high the first mosfets pulls EN_Q low which then in turn shuts off the other mosfet and enables EN_R to go high (leaves it floating) - EN_R itself needs to be pulled high from something else somewhere. Is this incorrect?

    Thank you.
    Attached Files
    Last edited by Prott; 08-10-2022, 05:54 AM.

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      #3
      Re: PS_NVVDD_EN_R low - circuit question

      Reading the datasheet of the buck controller (uP9511?) can help. EN is not pulled-up externally, external circuit leaves it floating to enable or pulls it to ground to disable. Since there's a resistor to ground which must be inside of a certain range of value, one can assume the chip has an internal current source on that pin, although it may not be active all the time.
      Last edited by piernov; 08-10-2022, 09:01 AM.
      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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        #4
        Re: PS_NVVDD_EN_R low - circuit question

        Thank you! I was reading the datasheet, but somehow skipped the part and it didn't occur to me that the buck controller produces its own enable signal.

        Time to check the soldering.

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          #5
          Re: PS_NVVDD_EN_R low - circuit question

          Fixed (it was a bad soldering job on the buck controller), thank you piernov!

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