• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 486 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DS90UB948-Q1: AC decoupling capacitor values when interfacing with 941 VS 947 serializers

Peter Bain
Prodigy 60 points
Part Number: DS90UB948-Q1

Hi,
In our design, we are using LVDS to FDP (DS90UB947) and DSI to FPD (DS90UB941). Rather than design 2 different display modules, we are trying to implement a single display that will work with either FPD output.
The issue is that different AC decoupling capacitors are specified for each of the serializers (we are using coax connection with both).
DS90UB947: DOUT+ is 33nF and DOUT- is 15nF
DS90UB941: DOUT+ is 100nF and DOUT- is 47nF

So for the DS90UB948 deserializer to to be compatible with either serializer, what value AC decoupling capacitor can I use on the deserializer FPD input signals as I am assuming this should be matched on both ends of the FPD connection.
Or can I use the same values on the 2 serializers? Say 100nF and 47nF for both and the same values at the deserializer end?

Regards,

Peter

  • 0
    TI__Mastermind 30515 points

    Peter,

    yes, you can use 100nF and 47nF in both de-ser. side, this cap. in de-ser, is serialized with the cap in the serializer side, they can be diff. values if they follow up TI's recommendation design in both d/s. The key point is that the cap. in negative pin should be ~ half of the cap in the positive pin, this is to make sure the symmetric in both positive and negative if you design single end transmission in the coax case.

    bet regards,

    Steven

  • 0 in reply to Steven(Shenzhen) Shi
    Prodigy 60 points

    Hi Steven,

    Thanks for the reply. Sorry, but to clarify:
    The capacitors do not need to match on each end of the FPD cable? For example, 100nF/47nF on the serializer, but 33nF/15nF on the deserializer side?

    Thanks, I understood the importance of the difference between positive and negative values being half.

    So I can stick to the data sheet recommendations for the serializers:
    DS90UB947: DOUT+ is 33nF and DOUT- is 15nF
    DS90UB941: DOUT+ is 100nF and DOUT- is 47nF

    And then use 100nF/47nF on the DS90UB948 deserializer?

    Regards,
    Peter

  • 0 in reply to Peter Bain
    TI__Mastermind 30515 points

    Peter,

    yes, it is correct. In your case, the total cap. between ub947 and ub948 is 133nf, and the cap between ub941as and ub948 is 200nf. both are ok..

    regards,

    Steven