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TPD12S521: about the sch for TPD12S521

Vera Mao
Expert 5065 points

Part Number: TPD12S521

hi dear supporting team,

could we remove the pull up circuit for CEC including the diode and 27k, 1.7K for I2C, HPD pull down 10K for below circuit?  (as below red circle in fig1 ).  fig2 is CEC, I2C,and PHD internal circuit. tks!

  • 0
    TI__Mastermind 34371 points

    I will break the answer down to each function:

    1.  The schottky diode and 27kOhm resistor are present to prevent reverse current flow into the 3.3V power supply and they cannot be removed to maintain compliance to the HDMI specification.

    2.  The 1.7 kOhm pullup resistors on DCLK and DDAT are necessary  to ensure that the DCLK and DDAT values are pulled up to the 5V logic supply of the HDMI connector in order to maintain compliance to the spec.

    3.  The 10 kOhm pull down resistor is necessary on the source side of an HDMI signal.  The protocol requires that the Sync pull this signal high to show that the connection has been detected.

    All of the passives shown in this diagram are necessary.

  • 0 in reply to Chuck Branch
    TI__Expert 5065 points

    Hi Chuck,

    thank you very much for the answer!

    customer stil has below questions:

    1. if they don't need qualified by CEC, and don't need CEC function, could they remove diode and the 27k resistor?

    2. if CEC don not connect the diode and 27k resistor, could they meet SPEC?

    3.  The circuit in below red circles, when LV supply is provided, they need pulling up at CE_REMOSTE_IN（IN SIDE）, do they need pull up at CE_REMOTE_OUT（OUTside）?

  • 0 in reply to Vera Mao
    TI__Mastermind 34371 points

    1.  The CEC_OUT port is typically connected directly to the HDMI connector, so if the pull up is not present, then CEC will not be biased to the correct voltage for the receiver on the opposite end of the connector.  If this lack of functionality is acceptable  and compliance to the HDMI standard is not required, then it is possible to remove these components.  I would advise against this decision because the solution will not mate with all possible HDMI receivers.

    2.  

  • 0 in reply to Chuck Branch
    TI__Mastermind 34371 points
    I apologize, I did not finish my response.

    The CEC line must meet the requirements listed in the table in the above response. There are conditions where CEC is not required, so it is possible that the connections may be omitted.

    3. The pull-ups are required on each side of the switch. They are referenced to different supplies. The output pins are referenced to 5V or 3V supplies as shown in the figure and the input signals are referenced to the LV supply. They must be pulled up as shown in the figure to function.