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DS90UB935-Q1: DS90UB935 to DS90UB954 - coax cable and AC coupling

Sunset
Genius 13375 points
Part Number: DS90UB935-Q1
Other Parts Discussed in Thread: DS90UB954-Q1,

Hello Team,

DS90UB935-Q1 to  DS90UB954-Q1 via coax cable and AC coupling, as the picture below:

The 33nF – 15nF capacitors are the smallest recommended.

  • Would it work with 22nF-10nF as well?
  • If the system works with 22nF-10nF is there anything preventing using it?

Thanks,

SunSet

  • 0
    TI__Guru* 98365 points

    Hello SenSet,

    We have never qualified operation with these devices using < 33nF/15nF AC coupling caps, so please stick with the design recommendation in the datasheet and use 33nF/15nF or 100nF/47nF caps.

    Best Regards,

    Casey  

  • 0 in reply to Casey McCrea
    TI__Genius 13375 points

    Thanks for the confirmation.

    But do you see any "no go" in going smaller capacitance?

    If the designer will do its own qualification and risk analysis (and take the risk), do you think it makes sense for the customer to qualify it?

    The system is a closed one and must not be compatible with other systems.

    Thanks,

    SunSet 

  • +1 in reply to Sunset
    TI__Guru* 98365 points

    Hello SunSet, 

    At a high level, reducing the capacitance may cause some issues with the FPD-Link back channel since the back channel operates at relatively lower speed which means that the bit widths are significantly larger than the forward channel bit widths. So you may see a reduction of the back channel eye width if the cap values are too low. For that reason I would suggest to stick with the datasheet for best performance. 

    Best Regards,

    Casey