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Original question:

DS80PCI402: DS80PCI402 1m FR4 PCB trace

DS80PCI402: number and location question

BX27
Genius 3900 points
Part Number: DS80PCI402

hi there

We are designing long PCIe3.0 x4  trace on three PCB boards as backplane architecture as below ( snapshot from datasheet ). Trace length on each  board is about 10cm ,so 30cm total.

BUT Ti mentioned in this post (https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1163085/ds80pci402-ds80pci402-1m-fr4-pcb-trace?tisearch=e2e-sitesearch&keymatch=DS80PCI402#)

that Not recommend TWO repeater on . which is conflict with the picture above.

So, will one DS80PCI402 be enough?  Should it be placed on CPU board, or backplbae board, or the FPGA board? If placed on backplane board, where should it be located? 

 

thanks.

  • +1
    TI__Genius 9209 points

    Hi BX27,

    Thank you for this question. I am going to investigate to find an answer and can get back to you on Monday Pacific US time.

    Best regards,

    Nick

  • +1 in reply to Nick Peabody
    TI__Genius 9209 points

    Hi BX27, 

    I recommend using the IBIS AMI model to simulate scenarios with one redriver in different positions on the trace. Some of the answer depends on your loss per cm. You can use this link to request the IBIS AMI https://www.ti.com/product/DS80PCI402#design-development

    Best regards,

    Nick

  • +1 in reply to Nick Peabody
    Genius 3900 points

    Hi Nick, thanks for replying.

    We generally use Low-loss pcb board material for PCIe application, whose loss is <0.5dB/inch @8GHZ.

    As you recommend to simulate with ONE redriver, why the datasheet use two redrievers in Typical Application Block Diagram on page one? 

  • +1 in reply to BX27
    TI__Genius 9209 points

    Hi BX27,

    No problem. I hope you're doing well. The application you mentioned would only need one redriver because the amount of loss from the trace length you stated is below the loss budget of one DS80PCI402. 

    As to your question about where to put the single redriver. It is recommended to place the redriver on the side with the highest loss, either the CPU or FPGA. Additionally, my recommendation to use IBIS AMI models for simulation still applies.

    It is not recommended to have two redrivers because the tuning is more difficult. The two redriver case is application dependent.

    Best Regards,

    Nick