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DS80PCI810: RX detect functionality in 85 ohm system

Jason Waln
Prodigy 130 points
Part Number: DS80PCI810
Other Parts Discussed in Thread: TIDA-00423

Hi

I have a desire to use the DSP80PCI810 in a hotswap 85ohm PCIe Gen3 application.

Has there been any testing with the DSP80PCI810 in an 85 ohm environment?  Differential traces are 85 ohms, Root complex and endpoints terminated at 85 ohms.

There's a sentence in the datasheet that states: "If 50 ohm impedances are seen on both positive and negative output of a DSP80PCI810 channel, Rx detect state machine asserts Rx detection".  So, what happens if 42.5 ohm +/-10% impedance is seen?  Will the Rx detect state machine still assert RX detection? 

Thanks,

Jason

  • 0
    TI__Mastermind 29655 points
    Hi Jason,

    Yes, we have successfully tested our DS80PCI810 in a PCIe system on a riser card (see TIDA-00423), which is an 85-Ohm environment.

    The Rx Detect state machine will still assert in an 85-Ohm environment. The Rx Detect state machine causes the Tx to send a pulse signal every 12 ms, and then our device measures the signal reflection to determine whether there is a termination after our Tx. If there is a termination, the reflected signal will be below an internally set threshold. This is true in the case of 42.5 ohms as it is with 50 ohms.

    Regards,

    Michael