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Original question:

DS80PCI800: Asking for the DS80PCI800 schematic review

DS80PCI800: The devices of both sides can only recognize the Gen1 but not Gen3

leo xue
Expert 1595 points
Part Number: DS80PCI800
Other Parts Discussed in Thread: DS80PCI810

Hello,

   My customer is using several DS80PCI800 as PCIE equalization and de-emphasis. 

The question is that the devices of both sides can only recognize the Gen1 but not Gen3.

Please refer to the block diagram below. The numbers on the line are cable length and the unit is millimeter.

The width of copper line is 6.5mil.  X1/X2 are the connectors.

Would you please give your hand on this ? How to make it recognize Gen3 signal?  thanks .

 


  • 0
    TI__Mastermind 43795 points

    Hi Leo,

    Based on the total trace length of approximately 60cm, the likely cause is over equalization.  I would recommend to set the equalization to minimum for all DS80PCI800 devices and set DEM = 0 dB as well.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Expert 1595 points
    Hi Lee,
    Thanks for your support.
    According to your advice, We have made great progress and system has already worked . But the eye diagram is not well.
    Now the PCIE can run in Gen3 speed, but the margin does not satisfy the requirements of Intel's test tool.
    According to your opinion, our problem is over equalization, does that mean the trace is too short? Can your give us some suggestion
    according to our total trace length.
    1, Should we use two DS80PCI800s in one trace? If it is essential, how should we place the two chips?
    2, If it is not necessary, and how should we place the chip?

    Regards,

    Leo
  • 0 in reply to leo xue
    TI__Mastermind 43795 points

    Hi Leo,

    I'm glad to hear your system is working.

    The minimum equalization from the DS80PCI800 is approximately 4 dB.  With two devices in series you have 8 dB of equalization from the devices.  This seems like too much for the trace lengths described.  I believe it is contributing to the low margin. 

    To improve the eye diagram I recommend to try the DS80PCI810 devices in place of the DS80PCI800.  These devices have less equalization and should improve the overall eye opening in this topology.  For the PCI810 I recommend the minimum equalization and VOD_DB = 0.

    Regards,

    Lee