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DS90UB913Q-Q1: problem with DS90UB913Q-Q1 back channel

Goran Fiolic
Intellectual 410 points
Part Number: DS90UB913Q-Q1

I have two identical serializer boards (I can provide schematic diagram) and I am experiencing problems when I try accessing serializer registers on one of the boards. I am always using the same deserializer board channel for testing the serializer boards, the same I2C access sequence, power supplies look O.K. board is connected to the deserializer board using coaxial cable, deserializer lock is present and stable, and FPD Link signal looks the same with both serializer boards (I can see backchannel low frequency signal and superimposed  high frequency forward channel signal). Serializer is using external 48MHz clock (mode pin voltage level is set accordingly). Is there any Link test I could preform (besides BIST) that could help me find what is wrong with the board.

  • 0
    TI__Genius 10475 points
    Hello,
    We received your question and this has been assigned for an Apps person to review.
  • 0 in reply to Palaniappan Manickam
    Intellectual 410 points

    In the meantime I run few more tests. Problematic serializer was connected directly to I2C master in order to check possibility of accessing serializer’s registers this way, and to read status register at address 0x0C.Serializer was accessible and the content of 0x0C register was 0x20, so it looks like there was no RX lock, and link was not detected (At the same time lock was detected at deserializer’s side and low frequency back channel signal was present - checked by oscilloscope). Datasheet states that revision ID for production version is 0x00 (at least that is my understanding of that data). From the 0x0C content it looks like serializer's ID is not that of the "production version". Could that be a source of the problem? I also checked a possibility that FPD Link power decoupling filter is causing the problem by disconnecting it from the line and by powering serializer directly, but the problem remained.

  • 0 in reply to Goran Fiolic
    TI__Guru* 83930 points
    Goran,

    yes, the production Revision is 0x0.
    did you try to check more 913A boards? how was the results?
  • 0 in reply to Hamzeh Jaradat
    Intellectual 410 points

    Hi Hamzeh,

    We have 30 boards and most of these boards work fine. The problem I described is present on 4 boards and we have to find what is causing it before we start a production of new set of boards. I know that problem may be PCB/component related but I can't find anything wrong with PCB or mounted components. Sometimes, when I2C initialization passes (with many errors, but I compensated that by adding retries to initi sequence) video transmitted through the forward channel is stable (no loss of lock at deserializer side). So, apparently, forward channel is fine, and only back channel is not working correctly. I speculated that power supply filter may be responsible (bad high inductance inductor for decoupling low frequency band), but after I disconnected filter from coaxial line and connected it directly to external linear power supply problem remained. So the only thing that I was able to find that looked suspicious to me was that revision ID number. Could that be the source of the problem? What is the difference between revisions 0x01 and 0x00?

    Regards

    Goran