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CDCLVD1204 - Unused output pin which has PCB trace

Kawai
Guru 19775 points
Other Parts Discussed in Thread: CDCLVD1212

Hello Team,

I believe unused output could be left open as described in the datasheet page 11.

Could you please advise us if we can keep unused outputs which has PCB trace on board ? Background of this question is that our customer uses common PCB design for 4 channel system and 2 channel system. Can we just keep unused output floating with PCB trace, or should we connect 100 Ohm termination ?

We would be appreciated if you could advise us by end of tomorrow, 10/25 Tuesday (PST).

Best Regards,

Kawai

  • 0
    Guru 19775 points

    Team,

    Could you please advise us how we should treat the output pins ? They need to fix design by tomorrow.

    It would be better not to add pcb trace on the unused output pins, however, as they use the same design for two systems they cannot change PCB design. When having such unused channels, what would you recommend ? Would it be better to keep floating or connect 100 Ohm termination resistor ?

    Best Regards,

    Kawai

  • 0 in reply to Kawai
    TI__Expert 4415 points
    Hi Kawai,

    I tested a similar setup on a CDCLVD1212 EVM where I looked at the output waveform and phase noise with and without the other device outputs terminated. Without termination, the floating traces are about 5cm long.

    I observed no difference in phase noise or signal integrity between the two cases. This is expected, as LVDS uses current mode drivers. Without a current path, there should be no differential voltage on the floating traces. So no termination is necessary.

    However, another factor to consider is anytime you have a floating trace, it can act as an antenna and let some noise couple onto it. There is a chance that the design might be noisier depending on the use case. Depending on how sensitive the application is to noise, the customer may consider terminating the traces anyway.

    Regards,
    -Tim
  • 0 in reply to Tim Chao Li
    Guru 19775 points

    Hello Tim-san,

    Thank you for your advise.

    Best Regards,
    Kawai