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SN65DP159: Internal intra-pair skew of TMDS OUTPUT pins

4606639
Prodigy 230 points
Part Number: SN65DP159

Hello,

 

I would like to ask a question for SN65DP159RSB.

For the intra-pair skew of each TMDS output pins,

how much intra-pair skew are existed between the external pin and the inside die of SN65DP159?

 

My product was checked whether it satisfies a compliance test items or not by Certification Authority.

As a result, I received the report which shown the product is not satisfied the item HF1-9.

HF1-9 is the test item related to the intra-pair skew of TMDS source lines.

 

I checked the PCB routing skew of each intra-pairs again.

But there are very small skew so I am wondering about the inside skew of SN65DP159RSB.

 

Can you please tell me the intra-pairs skew of each output pins?

Also, are there very small?

 

Best regards,

  • 0
    TI__Guru**** 178126 points

    Please see table 7-10, max intra-pair skew is 40ps with the following test condition:

    SLEW_CTL = NC; TX_TERM_CTL = NC; PRE_SEL = NC; OE = H; DR = 6 Gbps;

    Do you have common mode choke on the output? Having common mode chock on the output would help passing the intra-pair skew requirement.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 230 points

    Thank you for your prompt reply.

     

    I am setting SN65DP159RSB to Pin-strap mode.

    The following are each pin setting on my project.

    For SLEW_CTL setting, which setting should we use, NC or High?

    Do you have any idea?

    (Current Setting)

    - SLEW_CTL : High

    - TX_TERM_CTL : NC (No-pin)

    - PRE-SEL : NC

    - (EQ_SEL/A0 : High)

     

    For your question, there is no common mode choke between SN65DP159RSB and HDMI connector.

    There are TPD4E02B44 on each TMDS line near HDMI connector.

     

    Best regards,

  • 0 in reply to 4606639
    TI__Guru**** 178126 points

    Can you please try setting PRE_SEL pin to low and increase VOD to see if it helps with the intra-pair skew? 

    Adding -2dB de-emphasis provides the largest skew performance improvement, this would be the first tuning I try.

    For VOD, smaller Vsadj resistor will improve intra-pair skew performance while increasing output swing.

    If tuning PRE_SEL and VOD still not able to pass the intra-pair skew compliance test, we may need to add the common mode choke.

    Thanks

    David