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Multiple SN75DP139

Nabeel Khan
Intellectual 1455 points
Other Parts Discussed in Thread: SN75DP139, TMDS442

Hey Team,

Can I use two SN75DP139 chips to drive two HDMI monitors with the exact same data?

DP++ --------- SN75DP139 --- HDMI 1 with DDC.

               |---- SN75DP139 --- HDMI2 with NO DDC.

Thanks!

  • 0
    TI__Guru* 76130 points
    Hello,
    That implementation will have signal integrity issues.
    Every TMDS receiver will have 50ohm terminations installed, connecting two receiver to the DP139's output will cause the DP139 to "see" a 25ohm terminations.
    You will require to add a TMDS442.
    Regards
  • 0 in reply to Elias Villegas M.
    TI__Intellectual 1455 points

    "Looking at the TMDS422, it is unclear to me if I can route the same source to two sinks. If I do this what happens to the DDC I2C info from the two sinks ports when they are routed to the one source port?"

    "Also can I put my DP++ signals into the TMDS422 chip?"

    Thanks for your help Elias.

  • 0 in reply to Nabeel Khan
    TI__Guru* 76130 points
    Hello,
    The TMDS442 has the ability to output the same signal on both TMDS sink_channels, only one of them will have its DDC lines routed to the Source though.

    The TMDS442 can't take DP++, this would be a 2-chip solution.

    Regards
  • 0 in reply to Elias Villegas M.
    TI__Intellectual 1455 points
    How does the chip decide which DDC lines get routed and which do not? Same question for the HPD_SINK signals?

    Will this work if the HDMI signal has HDCP protection? (I am guessing it works for the main port (with DDC) but not the secondary port (no DDC) )

    Do we have a reference design and board available for this part?

    Thanks for the quick response!
  • 0 in reply to Nabeel Khan
    TI__Guru* 76130 points
    The TMDS442 will switch the TMDS lines and the DDC lines according to the SA and SB control pins. Look at SOURCE SELECTION LOOKUP Section in datasheet for more details.

    If HDCP encryption is used, this will not work. If the two monitors do not support the same resolution, this will not work.
    Yes, we do have an evaluation board, you can order one at the below link.
    Regards
    sps04.itg.ti.com/.../Active.aspx
  • 0 in reply to Elias Villegas M.
    TI__Intellectual 1455 points

    -Will the output of the TMDS442 chip be able to drive a 10 meter HDMI cable?

    -Does it have the same drive output as the SN75DP139?

    Thanks!

  • 0 in reply to Nabeel Khan
    TI__Guru* 76130 points

    Hello,

    Please see below answer from a previous post:

    "TMDS outputs on most of our devices are designed for internal use as an input switch for a video receiver.  It of course can be used as a source but there can be incopatibility issues with DDC signals as some of our devices use I2C redrivers (levels are shifted).  The "output drive" cababilities and the cable supported is really more of a receiver issue and not specifically associated with our device.  We will generate the appropriate voltage when the sink is attached (TMDS CML outputs require a 50 ohm termination to the common mode voltage) and the loss of the cable will determine the ISI generated as well as the amplitude at the end of the cable (the higher the gauge of the wire in the cable and the higher the data rate will have a higher loss and of course a longer the cable will also generate more loss).  Our device will only recondition the input signal by equalizing the input (compensates for the ISI loss on the input by equalization), but most of our newer devices have nothing for pre/de-emphasis on our outputs.

    This all being said, I use 8m 26 and 28 AWG cables in my lab all the time to connnect our EVM outputs to the various TV's with no high speed signal issues (most TV's have input equalization to compensate for cable loss).  For DVI systems, 5m 26 and 28 AWG should be fine with a good low loss input"