The new 3.3v and 5v Regulators i need a clarity here

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  • mnciks11
    Badcaps Veteran
    • Aug 2019
    • 345
    • south Africa

    #1

    The new 3.3v and 5v Regulators i need a clarity here

    Hello guys

    i was working on the new lenovo laptop with the new power supply for 3.3v and 5v, below on the picture i circled a resistor that was installed on the Vin power rail for the 3.3v always chip, but i dont understand the fuction and use of the resistor, why it was installed...Please anyone whose more advanced can assist please
    Attached Files
  • RethoricalCheese
    Badcaps Legend
    • Mar 2013
    • 1517
    • Estonia

    #2
    Re: The new 3.3v and 5v Regulators i need a clarity here

    That resistor is a pull-down resistor for the enable pin. But it is strange indeed because EN is connected to Vin. So I guess they had a design change but did not remove the resistor.

    Comment

    • mnciks11
      Badcaps Veteran
      • Aug 2019
      • 345
      • south Africa

      #3
      Re: The new 3.3v and 5v Regulators i need a clarity here

      Originally posted by RethoricalCheese
      That resistor is a pull-down resistor for the enable pin. But it is strange indeed because EN is connected to Vin. So I guess they had a design change but did not remove the resistor.
      Ey I was so confused my brother

      Comment

      • ktmmotocross
        Boardkiller
        • Feb 2014
        • 3578
        • slovakia

        #4
        Re: The new 3.3v and 5v Regulators i need a clarity here

        that pull dow resistor is for put voltage down fast from capacitors to fast swith down. if it was not there the capacitor can hold charge and EN signal will be active for long time.
        every en signal must have capacitor and resistor paralel to ground like EN1 signal

        Comment

        • SMDFlea
          Super Moderator
          • Jan 2018
          • 20695
          • UK

          #5
          Re: The new 3.3v and 5v Regulators i need a clarity here

          The resistor isn`t installed on some other compal boards,it could be a mistake in the schematic ,they didn`t mark it as @ no-stuff.
          Attached Files
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          Comment

          • mcplslg123
            Badcaps Legend
            • Jun 2015
            • 7262
            • india

            #6
            Re: The new 3.3v and 5v Regulators i need a clarity here

            I agree with @smdflea

            Comment

            • RethoricalCheese
              Badcaps Legend
              • Mar 2013
              • 1517
              • Estonia

              #7
              Re: The new 3.3v and 5v Regulators i need a clarity here

              Yup, I would say PR339 should not be @ and PR335 should be.

              Comment

              • mcplslg123
                Badcaps Legend
                • Jun 2015
                • 7262
                • india

                #8
                Re: The new 3.3v and 5v Regulators i need a clarity here

                Originally posted by RethoricalCheese
                Yup, I would say PR339 should not be @ and PR335 should be.
                Exactly. You find out the mistake in diagram.

                Comment

                • reformatt
                  Badcaps Legend
                  • Feb 2020
                  • 1401
                  • Australia

                  #9
                  Re: The new 3.3v and 5v Regulators i need a clarity here

                  Refer to the datasheet, enable pin is not meant to be left floating. So the 1M resistor ties that logic line to ground when no voltage is present. Prevents erratic operation when power is first supplied.

                  Comment

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