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HD3SS215: Switching converted HDMI signals (from DP or USBC)

Vera Ho
Prodigy 40 points
Part Number: HD3SS215

Hi!

I built up a prototype to switch between two HDMI sources and output to a display. It seems to work fine with sources that are initially HDMI outputs (from laptop or Chromecast). When I try to connect a source that's originally DP (using a DP to HDMI cable from a PC laptop), or USB C (Macbook Pro USB C to HDMI converter, then HDMI cable), the output is either black or very unstable. The source device registers that there's a second display connected. From the datasheet, it doesn't seem like the HD3SS215 chipset would differentiate between these since the signals have been converted to HDMI, but is there something more to it? The sources work on the display individually. 

Thank you!

  • 0
    TI__Guru 64326 points
    We are looking into your issue and will get back to you as soon as possible.
  • 0 in reply to Malik Barton57
    Prodigy 40 points
    A bit of an update after some troubleshooting:
    * The DP to HDMI might be the laptop's fault (it's older and may not be able to push 2 displays). It will show the desktop but once you try to do anything, it'll blink in and out.
    * For using a USB C adapter from the Macbook Pro, I found that initially it will be a black screen. If I change the resolution/color profile around, it will eventually come up on the display. Doesn't seem to be consistent on which resolution/color profile setting will get it to come up.

    So now it seems the MBP is the main issue I'm having. I measured the HPD on the sink side and it's 4.89V. On source HPDA and HPDB, I measure 3.19V and 3.14V respectively. Should there be such a difference in HPD measurements?

    Thanks!
  • 0 in reply to Vera Ho
    TI__Guru 64326 points
    Vera,

    There should not be such big difference measurements. Is it possible to post a schematic for this application? Also is HPDA and HPDB are low (~0 V) what do you see on HPDC?

    What kind of resolutions have you gotten to work with the Macbook Pro? There could be signal integrity issues due to USB-C to HDMI conversion and cabling. How long is this from the Macbook Pro cable to the HD3SS215?
  • 0 in reply to Malik Barton57
    Prodigy 40 points

    hdmi_switch_v0.03.pdf

    Hi Malik,

    When both A and B sources are not connected, the sink HPDC is measuring 0V. Once I connected something to source A, HPDA measures 3.08V now, HPDB measures 0V, and HPC measures 5.00V.

    The HDMI to HDMI cable is 6 feet long and is the same cable I use to test the HDMI to HDMI connection from a different source (that works with no problems). The USB C to HDMI adapter is about 6 in. It looks similar to this from Amazon:

    What I have tried with the MBP is to change the resolution/color profiles:

    • Black screen on monitor, but MBP recognizes the display
    • Change resolution to 720p instead of 1080p
    • Change color profile to generic RGB or sRGB
    • Display will mirror MBP
    • I can then change resolution and/or color profile back to default and the display will stay up
    • If I switch away from the MBP source, it will be black again next time I switch to MBP source and have to repeat the resolution/color profile process again
  • 0 in reply to Vera Ho
    TI__Guru 64326 points
    Vera,

    HD3SS215 is 5 V tolerant on HPD, your sink may be have a pull-up resistor to 5V causing this measurement. It seems that HPD is not the issue.

    Are you able to look into the Aux traffic between the MBP and the monitor? It seems that the MBP and monitor are link training in a configuration that does not allow for 1080p DP connection at first (ex 2 lanes of DP instead of 4 lanes of DP). You could confirm this by reading the Aux traffic, the USB C to HDMI adapter may be causing trouble in this regard.
  • 0 in reply to Malik Barton57
    Prodigy 40 points

    Unfortunately, I can't monitor the AUX traffic. Since it sounds like the issue is more the USB C to HDMI adapter or MBP and not the HD3SS215 chip or board design, I'm inclined to let it be. 

    Thank you!