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TMDS181: -

Jeevan Sidharth G
Prodigy 180 points
Part Number: TMDS181
Other Parts Discussed in Thread: TMDS171

Hi,

We have used TMDS181RGTZ in our design and have noted that when I plug a source into the HDMI port, the device gets detected. However, if I turn off the source and then turn it on, it does not get detected. That is, it is required for us to unplug and plug in the HDMI cable every time the device boots.

The above case is only noted when the source OS is Windows 11, it works fine when the source OS is windows 10.

Kindly guide us through getting the device to be detected without manual plugging3326.EXT_HDMI.pdf

  • TI__Guru**** 150235 points

    Hi,

    When the source is turned off, do you see EX_HDMI_HOT_DETECT signal going low?

    Thanks

    David

  • in reply to David (ASIC) Liu
    Prodigy 180 points

    Hi David,

    If I turn off the source, the signal remains high at 3.3V. However, if the PCB containing the re-driver is powered off, EX_HDMI_HOT_DETECT goes low and becomes high when it is turned on. EX_HOTPLUG_DETECT stays high in both cases.

    Thank you.

  • in reply to Jeevan Sidharth G
    TI__Guru**** 150235 points

    Hi,

    When the source is off, I would assume the EX_RX_5V_POW would go low as well. If this is the case, can you make sure the Scaler drive the EX_HOTPLUG_DETECT low?

    Thanks

    David

  • in reply to David (ASIC) Liu
    Prodigy 180 points

    Hi,

    Sorry for the wrong information in the previous reply, if the source is off the HOTPLUG works fine. But if the source is on and the redriver is powered off and on, it does not get detected.

    When the source is on and the redriver is powered off, EX_HOTPLUG_DETECT remains high.

    When the source is on and the redriver is powered on,EX_HOTPLUG_DETECT goes low for a few ms and then is pulled high(not working).

    Thankyou.

  • in reply to Jeevan Sidharth G
    TI__Guru**** 150235 points

    Hi, 

    For the EX_HOTPLUG_DETECT, I assume it is driven by a sink directly to the TMDS181 and the HDMI connector? If this is the case, is the sink capable of driving the EX_HOTPLUG_DETECT 5V?

    Can you disconnect TMDS181 HPD_SRC from EX_HDMI_HOT_DETECT? The absolute max rating for HDP_SRC is 4V and TMDS181 will get damaged when being driven with 5V.

    With TMDS181 HPD_SRC disconnected from EX_HDMI_HOT_DETECT, and if you remove the below 1k resistor, do you still see the issue?

    Thanks

    David

  • in reply to David (ASIC) Liu
    Prodigy 180 points

    Hi,

    Even after making the above changes, I can observe the same issue.If I am not wrong, the HPD is driven using the 5V from the source side.

    The EX_HOTPLUG_DETECT is connected to ADV7611.

    So according to my assumption, as soon as a source device is connected to the HDMI connector,EX_RX_5V_POW signal gets 5V and this 5V goes through the 1k resistor, and from the voltage divider, around 4.8V goes to EX_HOTPLUG_DETECT.

    Thankyou.

  • in reply to Jeevan Sidharth G
    TI__Guru**** 150235 points

    Hi,

    Can you please remove the 1k and let ADV7611 drive HPD? The implementation will look like this.

    You can also keep 1k, but not let ADV7611 driving it. For TMDS181, HDP_SRC needs to be floating, and HPD_SNK needs to be pulled up.

    Thanks
    David

  • in reply to David (ASIC) Liu
    Prodigy 180 points

    Hi,

    If the 1k is removed, there is no voltage noted at EX_HOTPLUG_DETECT, and 3.3V is noted at HPD SRC.

    Thankyou.

  • in reply to Jeevan Sidharth G
    TI__Guru**** 150235 points

    Hi,

    The TMDS181 HPD_SRC is driven by the TMDS181 HPD_SNK. The HPD_SRC basically level shifts from 5V HPD_SNK down to 3.3V. But if EX_HOTPLUG_DETECT (which is connected to the HPD_SNK) has no voltage, then I don't see how HPR_SRC can be 3.3V. 

    I assume when there is no voltage at EX_HOTPLUG_DETECT, the device does not gets detected?

    The ADV7611 has a HPA_A/INT2 pin, is it connected to EX_HOTPLUG_DETECT? 

    Thanks

    David

  • in reply to David (ASIC) Liu
    Prodigy 180 points

    Hi,

    Yes, the device does not get detected when there is no voltage at EX_HOTPLUG_DETECT and the ADV7611 is connected to EX_HOTPLUG_DETECT.

    Even when there is no source connected to the HDMI, as you have told I can observe 3.1V at EX_HDMI_HOT_DETECT which might be driven by HDP_SRC.

    Will the ADV7611 HPA_A assert 3.3V always? 

    Thank you.

    Regards,

    Jeevan.

  • in reply to Jeevan Sidharth G
    TI__Genius 13290 points

    Hello,

    I am reviewing this thread and will get back to you shortly.

    Thanks,

    Zach

  • in reply to Zach Dryer
    Prodigy 180 points

    Hi Zach,

    I am additionally attaching the schematic of the ADV7611 for a better understanding.

    ADV_TMDS181.pdf

    Regards,

    Jeevan

  • in reply to Jeevan Sidharth G
    TI__Genius 13290 points

    Jeevan,

    Thank you! 

    Thanks,

    Zach

  • in reply to Zach Dryer
    TI__Genius 13290 points

    Jeevan,

    Did you try to remove the 1k resistor (R267) and let ADV7611 drive HPD? 

    I am not sure since it is still in the schematic you shared with me.

    Thanks,

    Zach

  • in reply to Zach Dryer
    Prodigy 180 points

    Hi Zach,

    Even after removing the 1k resistor, the result remained the same. I am unable to observe the ADV7611 driving the HPD in any case. After removing the 1k resistor (R267) and FB48, only 3.1V is observed in EX_HDMI_HOT_DETECT (HPD SRC) and not in the EX_HOTPLUG_DETECT, making it clear that the ADV7611 is not driving the HPD.

    Regards,

    Jeevan

  • in reply to Jeevan Sidharth G
    TI__Genius 13290 points

    Hello, Jeevan,

    There has to be a voltage at the HPD_SNK pin for there to be a voltage on the HPD_SRC. The TMDS171 device simply passes the HPD signal through.

    The only place in your schematic that you are driving signal with the 1k resistor (R267) and FB48 being removed is the ADV7611.

    Thanks,

    Zach

  • in reply to Zach Dryer
    Prodigy 180 points

    Hi Zach,

    If there is no source device connected to J28, should I still observe 3.3V at HPD_SNK?

    Regards,

    Jeevan

  • in reply to Jeevan Sidharth G
    TI__Genius 13290 points

    Hi, Jeevan,

    If no device is connected to the J28 connector then your source should not observe the HPD_SNK coming from the ADV7611.

    If this is the issue you are seeing, please consult with the ADV7611 manufacturer.

    Thanks,

    Zach 

  • in reply to Zach Dryer
    Prodigy 180 points

    Hi Zach,

    If no HPD is observed, then why is it said that HPD is driven from ADV7611?

    From my understanding, HPD is a detect signal sent from the sink to the source and is driven by the sink(ADV7611 in this case). If 3.3V is not observed always, then how will the source be detected as soon as it is connected?

    Regards,

    Jeevan

  • in reply to Jeevan Sidharth G
    TI__Genius 13290 points

    Hello, Jeevan,

    The HPD is asserted only when the 5 V power line from the source is detected. Therefore, if no device is connected to the J28 connector then your source should not observe the HPD_SNK coming from the ADV7611.

    If this is the issue you are seeing, please consult with the ADV7611 manufacturer.

    Thanks,

    Zach

  • in reply to Zach Dryer
    Prodigy 180 points

    Hi Zach,

    When no device is connected to the J28 connector, no voltage is observed at HPD_SNK, as mentioned in our case.

    Could you confirm if the following observations align with expectations?

    1. Without any device connected to J28:

      • HPD_SRC measures 3.1V
      • HPD_SNK shows no voltage

    2. When a source device is connected to J28:

      • HPD_SRC measures 3.2V
      • HPD_SNK measures 4.8V

    Let me know if this matches the expected behavior.

    Thankyou

    Regards,

    Jeevan

  • in reply to Jeevan Sidharth G
    TI__Genius 13290 points

    Hello, Jeevan,

    I am looking into this and will get back to you.

    Thanks,

    Zach

  • in reply to Zach Dryer
    TI__Genius 13290 points

    Hello, Jeevan,

    You can check that there good isolation on your HPD pin from any of your power planes or pins.

    What you are seeing is not expected since expected behavior is as follows:

    1. Without any device connected to J28:

      • HPD_SRC measures 0 V
      • HPD_SNK shows no voltage

    2. When a source device is connected to J28:

      • HPD_SRC measures 3.3V or 5 V (if you use the HPD 5V implementation shown in Figure 35. TMDS181 in Sink Side Application (Including 5 V HPD Implementation))
      • HPD_SNK measures 3.3 V

    Here is a more in-depth table that you can follow:

    I am closing this ticket since the problem seems to be systematic and not related to our device.

    Thanks,

    Zach