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CDCDB803: Parallel Clock Buffer

Johann Fort
Prodigy 140 points
Part Number: CDCDB803
Other Parts Discussed in Thread: LMKDB1120,
Hello,

I am looking to use two clock buffers in parallel with two CDCDB803 components.
Inputs are connected to a PCIE Gen 4 clock
 


Is this setup feasible?

How can I optimize this assembly?

Best regad,
Johann
  • 0
    TI__Genius 10975 points

    Hello Johann,

    What is the source of your PCIe Clock? Do you need phase alignment or synchronization among your outputs? From my understanding, phase alignment between all clocks is not required for PCIe, but please correct me if I'm wrong?

    Overall, yes you can use 2 CDCB parts to fan out your PCIe clocks, but do clarify my questions to give you an accurate response. Thanks!

    Best,

    Andrea

  • 0 in reply to Andrea Vallenilla
    Prodigy 140 points

    Hello Andrea,

    The source is the Intel processor which generates a PCIe Gen 4 reference clock of 100Mhz in x8 (8.0 GBit/s)

    The extract of Reliability Report "To Measure PCI-e Reference Clock With Multiplexers" :



    The PCIe standard specifies a 100 MHz clock (Refclk) with at least ±300 ppm frequency stability for Gen 1, 2, 3 and 4.

    Best Regard,
    Johann

  • 0 in reply to Johann Fort
    TI__Expert 8231 points

    Johann,

    Andrea is out of the office, but I believe you can use 2 CDCB parts to fan out your pcie clocks.  I will get back to you tomorrow to confirm that this is the ideal configuration. 

    Regards,
    Will

  • 0 in reply to William Pfennigwerth
    TI__Expert 8231 points

    Johann,

    Sorry for the delay.  I will try to get an answer to you by tomorrow.

    Regards,

    Will

  • 0 in reply to William Pfennigwerth
    TI__Expert 8231 points

    Johann, 

    Sorry for the delay due to the US Holiday.  After looking into your setup more, it would be better to use a single LMKDB1120 with 20 outputs and leaving 4 outputs floating instead of the two CDCDB803.  The drawbacks of using two CDCB803s is that you will have two ICs, more routing for your layout, and some potential signal degradation problems doing vias to get two input lines.  The LMKDB1120 is also more ideal in that it will only require a single IC so you will not have to worry about having two power supplies, the output skew, and part to part skew.  

    Sorry for delay, and let me know if you have any more questions,

    Will