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SN65DP159 TMDS Sink AVCC requirement

Other Parts Discussed in Thread: SN65DP159

Hi,

What is the minimum DC voltage we need to have on the SN65DP159 TMDS data lines for the IC to work correctly? Will I be able to get a good signal integrity on TMDS lines if the AVCC on the sink is 2.1V (rather than 3.3V as recommended by the HDMI spec)?

Thanks,

  • Hi Rajan,

    In datasheet section 7.7, you can see electrical characteristics for TMDS outputs, use it as reference for how much you can lower the voltage in TMDS outputs.
    The problem having a low voltage on TMDS pins is that you may have a different polarization in current sources, leading to incorrect behavior.

    Regards
  • Hi Moises,
    Thanks for your response! The voltages in section 7.7 are specified with respect to VCC but the VCC is not specified. Is this true only for 3.3V VCC? What if the VCC on the sink side is 2 V?

    Thanks,
    Rajan
  • Hi Rajan,

    This device has Vcc min=3V,
    Lowes output voltage on TMDS pins is Vcc-1V=2V (3.4-Gbps< Data rate < 6-Gbps; PRE_SEL = NC; TX_TERM_CTL = L; SLEW_CTL = H; OE = H; R = 6-Gbps)
    Output swing range for data lanes is 400mV to 600mV, for clock lane is 200mV to 400mV.

    So, taking 2V as our lowest supported voltage on TMDS output pins and 400mV as the smallest output swing, the minimum suported Vcc on sink device would be 2.4V

    Having a 2V Vcc on sink device is not a standard application so we don't support it. If you have 2V plus 500mV output swing, voltage on TMDS output pins would dropt to 1.5V, this could lead to wrong polarization of current sources.

    You may try placing 50 ohm pullups, then 0.1uF AC cap if your device supports AC coupled signals.

    Regards