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DS80PCI800: PCIe GEN3 redriver/retimer suggestion

Terry Wu2
Expert 2110 points
Part Number: DS80PCI800
Other Parts Discussed in Thread: SN75LVPE802, DS80PCI810, , SN75LVPE801, DS125BR111, DS80PCI102

Hello Sirs,

We have a case need PCIe GEN3 redriver/retimer for long distance as attach picture.

Would you pls give me a comment could ds80pci8xx or SN75LVPE802 ok for this case ?

Many thanks !

  • 0
    TI__Mastermind 29635 points

    Hi Terry,

    Looking at your system, the maximum distance that you will need to support is 29", and the minimum you would need to support is 18". For these types of lengths and assuming FR4 material, you can use either the DS80PCI800 or DS80PCI810 for 8-channels unidirectional for the ports that are beyond the limits that are currently capable between your PCH and endpoint. 

    We typically recommend placing the redrivers closer to the Rx side of the signal path in order to allow the signal to pass through to the endpoint as linearly as possible.

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Expert 2110 points

    Hello Michael,

    Thanks your suggestion ! Yes for FR4 PCB material.

    For max length 29" . Where redriver placed in between PCH and endpoint ? 

    PCH -> 20" ->Redriver -> 9" -> endpoint ?  

    Many thanks !

  • 0 in reply to Terry Wu2
    TI__Mastermind 43795 points

    Hi Terry,

    The placement sounds okay.  We prefer to have the repeaters closer to the receive side on all channels if possible.

    Best Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Expert 2110 points

    Hi Lee,
    Many thanks your comment !
    I check another post show DS80PCI810 and DS80PCI800 difference is PCI810 without output de-emphases .
    May I know how long distance can be handle behind re-driver PCI800 and PCI810 ?

    And due to we have PCIe GEN3 x1 for 16 riser card . Prefer to consider SN75LVPE801/802 .

    Do you have suggestion using LVPE801/802 ?  <= Datasheet show support over 24 inch FR4 trace .



    TKS !

  • 0 in reply to Terry Wu2
    TI__Mastermind 43795 points

    Hi Terry,

    I would recommend the DS80PCI102 or DS125BR111 for this PCIe x1 application.  I would not recommend using the LVPE801/2.

    The DS80PCI102 works like the PCI800.  The DS125BR111 works like the PCI810. 

    In general the DS125BR111 or DS80PCI810 provide more repeater placement flexibility.

    What is the total channel loss in this application?  For approximate loss is ~ 0.8 dB/inch, for a 29 inch channel this is ~ 23-24 dB.

    Does this loss include attenuation from any add-in-card as well?

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Expert 2110 points
    Hello Lee,
    Many thanks your suggestion !
    Yes the DS80PCI102 have more EQ gain 36 dB than SN75LVPE802 15 dB. The IC cost still a problem .
    SN75LVPE802 DS page 1 show " Excellent jitter and loss compensation Capability for 24 inch FR4 " ... Is this not correct ?

    Does this loss include attenuation from any add-in-card as well? <= Not include
  • 0 in reply to Terry Wu2
    TI__Mastermind 43795 points

    Hi Terry,

    The SN75LVPE802 is not recommended for new PCIe designs.  It does not support the receiver detect function which can be a barrier for successful operation.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Expert 2110 points
    Hi Lee,
    Sounds this is a problem .. Can any extra discrete component could improve it ?
    Will new version of LVPE802 fix this issue ? Or need to remove PCIe support from DS ?
    Currently the LVPE802 design on riser card side (Port 0~Port15) .
    TKS !
  • 0 in reply to Terry Wu2
    TI__Mastermind 43795 points
    The extra pulldown resistors in the schematic are designed to emulate a PCIe receiver to GND. However this will not always work. If it does not work there is no fix or updated version of the LVPE802 to correct the issue.

    Regards,
    Lee