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TMDS181: TDMS channel not working.

Choi HyunWoo
Prodigy 40 points
Part Number: TMDS181

Hi.

This is a question related to TMDS181.

I have configured the circuit using TMDS 181, and HPD HDCP works normally, but the TMDS channel does not seem to work.

I'm not sure if it's a circuit configuration mistake, so please check it.

  • 0
    TI__Guru**** 177301 points

    Hi,

    I would tie SDA_CTL and SCL_CTL to 3.3V through 10k resistors.

    But if you are AC coupling the TMDS181 output, then you would need to provide external 50ohm termination to 3.3V between the TMDS181 output and the AC coupling capacitor since HDMI is a DC-coupled 3.3V bus.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 40 points

    I am trying to drive without using I2C communication, but is the TMDS181 output only when the SDA_CTL and SCL_CTL pins are connected?

    Is this an external 50ohm termination to 3.3 between the TMDS output and the AC coupling capacitor?

  • 0 in reply to Choi HyunWoo
    TI__Guru**** 177301 points

    Hi,

    Even without I2C communication, I would still tie these two pins to a certain state since they are inputs. But tie them high does not impact the no output issue.

    For the no output issue, you need 50ohm to 3.3V as you show in your schematic, and you need them on all data and clock output, both positive and negative.

    The other thing is that the pullup on SDA_SNK and SCL_SNK need to be 2k per the HDMI spec, but this is a separate issue from the no output issue.

    Thanks

    David