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DisplayPort SN75DP118 power

Aaron LeClaire
Prodigy 140 points

Other Parts Discussed in Thread: SN75DP118, SN75DP119

Hello,

The SN75DP118 supply voltage is 5V.  Does this need to come from a linear, or is a switching supply okay?

Thanks!

Aaron

  • 0
    TI__Expert 6745 points

    A switcher is probably okay if you make sure proper bypassing and filters are used, but of course any modulation of the power rail could cause jitter (AM as well as PM) on the output signal.  We don't normally spec PSRR for our devices. We do have some filtering internal to help with this issue on the input power.  A linear would almost always provide a cleaner rail for the device.

    Ken

  • 0 in reply to Ken Shaw
    Intellectual 270 points

    Hi ken,

         I use SN75DP118 on my board between DPRx connector and DP receiver chip as PCB trace is about 10 inches long.

        I am debuging the board right now, the input signal to DP118 looks okay, but output signals of DP118 look bad (the eye is close).

        I only use one lane and left other lanes un -connected, but I do pull LPn and HPD_IN to HIGH. ---------------------- Is this wrong?

        I was trying to use SN75DP119 for this application, however DP119 is a eDP repeater. As my understanding, eDP has a little difference between regular DP.

       Do you think DP119 is okay for driving longer PCB traces on regular DP application?

     

       Do you have EV boards for DP118 and DP119?

     

    Thanks,

     

    Tony   

  • 0 in reply to Tony51646
    TI__Expert 6745 points

    The DP118 is really more of a voltage follower with a very small amount of ISI compensation.  It's main design topology is a few inches of PCB trace on the input and the DP connector on the output.  The DP120 has the same foot print, but is a full rederiver, but again, mainly designed for the source application and not necessarily for the receiver environment.

     

    Leaving the DP118 inputs un-connected can be a problem if noise is present in the system.  The inputs can have a significant differental "gain" and could possibly be causing some issue.  It is recommended that unused inputs have a fail safe circuit installed (1k pull down on the inverting input) to insure good operation.

     

    Is this application of the DPRx connector an internal link or generic DP interface?  For the DP119 to operate in your configuration, the DP interfaces need to be fixed and known both on the input an output and a known video resolution as there is no link training through the DP119.  The DP119 has only fixed input and output pin configurations for equaliztion and voltage settings with only 2 lanes for the DP signals (instead of the all 4) unless two DP119 devices are to be used.

     

    We do have DP118 EVM's available, but nothing for the DP119 as it is normally connected to an internal non-standard DP interface for both the input and output.

     

     

     

     

  • 0 in reply to Tony51646
    Prodigy 140 points

    Tony,

    Please email me at aaron.leclaire@barco.com.   I have a recommendation for you.

    Aaron

  • 0 in reply to Ken Shaw
    Intellectual 270 points

    Hi Ken,

          My application is a generic DP interface, not a eDP interface, as I know  the scrambler seed is different between these two applications.

         So I am wondering that I can't use DP119 in generic DP application.

     

    Thanks,

     

    Tony

  • 0 in reply to Tony51646
    TI__Expert 6745 points

    The DP redriver product line do not change the data, but rather reshape the data to be compliant.  Scrambling is done at the source and unsrambled by the receiver.  We do not have any clock recovery or data retimer.

     

    The DP119 is not really designed for the generic DP interface.  It was designed for a notebook type of application to reshape the signal from the GPU on the mother board to the TFT panel.  It does not participate in link training and is only controlled by the equalization, Vod settings, and pre-emphasis control.

     

    What issue is trying to be solved by this inquiry?  It sounds like there is a standard DP interface with a receiver that is not working?  Is the DP receiver not capable of supporting DP loss profile of the link?  Normally, the DP products we support would go in the source and the DP link would negotiate the number of lanes, Vod,  and pre-emphasis level to support the link.