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TDP158: Compliance test for VL is failed

ttd
Mastermind 8600 points
Part Number: TDP158

Tool/software:

Dear Technical Support Team,

My configuration is HDMI1.4b.

HDMI compliance test result is failed due to VL=approx. 2.5V. The others test are passed.

I changed Vsadj from 6KΩ to 6.49KΩ, but it doesn't work for increasing the level over VL=2.6V.

So I set TERM following and got VL=2.6V.

Current setting is TERM =high(for HDMI2.0) ⇒ VL shows approx. 2.5V

Change TERM =NC(forHDMI1.4b)⇒VL shows approx. 2.6V

Questions:

①Could you show me the reason why VL is increasing for HDMI1.4 with VL=NC?

②Which is better for following configuration?

TMDS_CLOCK_RATIO_STATUS=0 and TERM=NC⇒ no termination(HDMI1.4b) ⇐Current setting VL=2.6V

TMDS_CLOCK_RATIO_STATUS=0 and TERM=L ⇒ 150～300Ω(HDMI1.4b) ⇐ Not yet

Best Regards,

ttd

  • 0
    TI__Mastermind 39375 points

    Hi,

    The range of differential termination for HDMI1.4 is open - 150ohm. 

    The range of differential termination for HDMI2.0 is 150ohm -75ohm.

    When using the HDMI2.0 termination with a signal that is expecting a higher differential termination (HDMI1.4) there will be an improper impedance which will led to a decreasing the swing level. This decrease may not be large enough to fail an eye diagram, bit it may be enough to change the swing level from 2.5V -2.6V as you have seen. 

    I recommend using the 150-300 ohm termination setting. 

  • 0 in reply to Vishesh Pithadiya
    Mastermind 8600 points

    Thank you for your response.
    By the way, my board does not use the CEC function of HDMI.
    The CEC pin (pin 13) of the HDMI connector (CN3) is left open.
    If the CEC function is not used, which is more suitable, open or GND connection?

  • 0 in reply to ttd
    TI__Mastermind 39375 points

    Hi,

    Either should be fine. I recommend grounding