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TMDS181: HPD feature

Antony Lin
Genius 13480 points
Part Number: TMDS181


Hi,

Will you suggest how can we decide if we need to use HPD_SRC/HPD_SNK or not?  If not, how should we connect these two pins with the chip?

Thanks!

Antony

  • 0
    TI__Mastermind 23815 points

    Hi Antony,

    HPD_SNK is needed for automatic low power mode, you can disable it if you don't need it.

    HPD_SRC is a buffered output of HPD_SNK, but Voh = 3.3V.

    For source applications, this voltage may be what the GPU needs.

    For sink applications, you need HPD to be 5V at the HDMI connector, so, you can add a level shifter, or use HPD snoop mode.

    Regards

  • 0 in reply to Moises Garcia
    TI__Mastermind 23815 points
    Hi Antony,

    I have to make an errata:
    HPD_SNK is needed for the TMDS181 to turn on.

    Regards
  • 0 in reply to Moises Garcia
    TI__Genius 13480 points
    Hi Moises,

    i dont' fully understand it. Since you mentioned HPD_SNK is needed for TMDS181, and HPD_SINK needs to be 5V at HDMI connector, cam customer add a external pull up (e.g. 1kohm) to 5V on HPD_SNK? If so, how about HPD_SRC? Keep it NC?

    Antony
  • 0 in reply to Antony Lin
    TI__Mastermind 23815 points

    Hi Antony,

    In HPD snoop mode, HPD_SRC can be left NC.

    Having HPD_SNK tied to 5V using a 1k resistor will have the drawback of increased power consumption and TMDS181 won't be able to reset itself when sink/source are disconnected.

    Regards

  • 0 in reply to Moises Garcia
    TI__Genius 13480 points

    Hi Moises,

    Thanks for the reply.  So, please help me to clarify something.

    1. How to judge if customer should use HPD_SNOOP mode or not?
    2. For case of using HPD SNOOP mode, how should they connect HPD_SNK and HPD_SRC on their board?
    3. For case of not using HPD SNOOP mode, how should they connect HPD_SNK and HPD_SRC on their board?

    Antony

  • 0 in reply to Antony Lin
    TI__Mastermind 23815 points

    Hi Antony,

    1. Snoop mode is mainly used when you don't want to place a level shifter at HPD_SRC from 3.3V to 5V.

    2. HPD snoop mode, connect HPD_SNK directly to HDMI receiver/connector, HPD_SRC=NC

    3. Not HPD snoop mode, connect HPD_SNK directly to HDMI receiver/connector, HPD_SRC to a level shifter, output from level shifter to HDMI connector. If HPD_SRC goes to the GPU the level shifter may no be needed.

    Regards