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DS125BR401: PCIe link up problem with external mux/demux

esevcar
Prodigy 10 points
Part Number: DS125BR401

Tool/software:

Hi team!

We have a problem bringing up a PCIe link that has the DS125BR401 and a mux/demux (PI3PCIE3412A) between the Root complex and the Endpoint. The block diagram of the path between the redriver and the Endpoint is:

 

We know the link works fine if the mux/demux is bypassed. We suspect that the problem might be the common voltage of the differential pairs. The mux/demux has the following electrical characteristics:

In the datasheet of the DS125BR401 it is stated that the inputs are terminated to VCC (CML input), so that DC component would reach the mux/demux as there is no coupling capacitors between them. Is that right? Could adding those capacitor fix the issue by isolating DC voltage levels?

Thank you!

  • 0
    TI__Guru* 93670 points

    Greetings,

    Cap should be on the DS125BR401 IN pin as you have shown in the diagram. I see the Cap before the mux/demux at PET. Just want to make sure we are isolating output common mode voltage of the mux part going to DS125BR401 part.

    Regards, Nasser