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  • Resolved

TPD12S520: TPD12S520:HPD with pull-up registor

Part Number: TPD12S520

Dear support team;

There is the following schematic in datasheet.

I designed by same schematic,Soc detected always HPD.

Becase there are pull-up registors with HDP line.(red circle)

Could you tell me why these registors need?

Best Regards,

 Masaaki Sugiyama

  • Masaaki,

    The HPD path has a level shifter internal to the chip that relies on the presence of these resistors to set the signal level.

    Regards,
    Chuck
  • In reply to Chuck Branch:

    Dear Chuck-san;

    Thank you for your reply.

    I understood the role of registors.

    I want to disconnect these registors.

    Becase, Soc detected always HPD.

    Is there any problem?

    Best Regards,

     Masaaki Sugiyama

  • In reply to Masaaki Sugiyama68:

    Masaaki-san,

    Removing these resistors will not impact the rest of the design. As long as you do not need the HDP functionality in your system, you may remove these resistors.
  • In reply to Chuck Branch:

    Dear Chuck-san;

    Thank you for your kindly support.

    I understood it.

    Best Regards,

     Masaaki Sugiyama

  • In reply to Masaaki Sugiyama68:

    Dear Chuck-san;

    I am sorry for my mistake.
    I use HPD.
    When HDMI cable does not connect, HDP signal is always HIGH, becase pull-up registor connect.
    So, Core Scaler Chip always detect HDP.
    I think that the pullup registor is not neccesary.
    How about do you think?

    Best Regard,
    Masaaki Sugiyama
  • In reply to Masaaki Sugiyama68:

    Masaaki,

    HPD should be pulled down by the consuming device when connected. The pull-down is used to differentiate between a floating signal (The 5V you are detecting) and the connection signal when the cable is plugged in.

    If you don't have the pull-up, you will lose this functionality.

    Regards,
    Chuck
  • In reply to Chuck Branch:

    Dear Chuck-san;

    My system is the following figure.

    When the PCB board is not provided Power, Source side always detects HPD high.

    So, I want to remove the 1K-ohm pull-up registor.

    Best Regards,

     Masaaki Sugiyama

  • In reply to Masaaki Sugiyama68:

    Masaaki-san,

    If you want to remove the resistor, then I would suggest using a low side nfet switch driven from the cable 5V supply so that the resistor is present when the cable is connected and then switched out when it is not. This way you retain the full function of the device.

    Regards,
    Chuck
  • In reply to Chuck Branch:

    Dear Chuck-san;

    Thank you for your kindly support.

    Best Regards,

     Masaaki Sugiyama

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