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SN75LVPE802: Redriver placement

Shota Mago
Expert 8110 points
Part Number: SN75LVPE802

Tool/software:

Hi team,

My customer considers to use SN75LVPE802 as a redriver for PCIe. One side of the redriver is connected to a connector which is connected to other equipment.

Regarding placement of the redriver, it should be placed close to connector and below diagram(and max trace length value) can be used as reference?

Best regards,

Shota Mago

  • +1
    TI__Mastermind 18830 points

    Hi Shota,

    The reference diagram is a decent approximate placement to start with, but I will explain the general principle: for a bidirectional redriver like the SN75LVPE802, we typically suggest that the redriver should be placed approximately in the middle of the loss channel, so that there is roughly similar insertion loss between the PCIe root complex and the redriver, and between the redriver and the PCIe endpoint. This helps ensure that the EQ behavior on the signal output is approximately similar in the upstream and downstream data directions. In the reference diagram, we see the redriver is placed closer to the connector side and is farther from the SATA host, but I expect this is because there should be more loss after the connector, so that the total loss before and after the redriver is quite similar.

    Most insertion loss in a PCIe link is typically from trace length, so the balance of trace length before and after a redriver is sometimes an OK estimate of where the middle of the loss channel might be, but there is also loss from connectors and from the packages/PCBs used by PCIe root complexes and endpoint devices that is not related to trace length. On our newer PCIe products, we have generally avoided discussing about trace lengths and focus on insertion loss instead. Typically customer SI engineers should be familiar with insertion loss calculations and can perform this analysis for redriver placement.

    Best,

    Evan Su