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LMK00334: LMK00334 || PCIe module not detecting

Yogishwari Shanmukhappa
Prodigy 30 points
Part Number: LMK00334

Hi TI team,

We are using LMK00334 in our design, below is the circuit diagram and the captured clock waveform (CH1 - PCIe_REFCLK_P, CH3 - PCIe0_REFCK_N, CH4 - PCIe1_REFCK_P).

PCIe reference clock (PCIe_REFCLK_P) is generated from the processor of other board and terminated on this buffer using board to board connector.With this circuit PCIE module is not detecting. 

When buffer is bypassed (as shown in the below image), one of the modules is getting detected. Do you have any feedback on this, please support us on the same.?

Regards,

Yogishwari

  • 0
    TI__Genius 9260 points

    Hi Yogishwari,

    HCSL output needs 50 ohm to ground DC path. Can you confirm if the customer has (R203- R206) populated on the board. It seems that its DNI on the schematic. If we don't have these then we won't see proper swing from HCSL output of buffer.

    Let me know if this is the case. It would solve this problem.

    Best,

    Asim

  • 0
    Prodigy 30 points

    Hi Asim, 

    Thanks for your reply.

    We changed (R203 - R206) with 50-ohm resistors, we are able to detect only one PCIe module (PCIe1_REFCK_P & PCIe1_REFCK_N) but we are not able to detect other PCIe module (PCIe0_REFCK_P & PCIe0_REFCK_N). below is the captured clock waveform (CH1 - PCIe_REFCLK_P, CH3 - PCIe0_REFCK_N, CH2 - PCIe1_REFCK_P).

    Please support us.

  • 0 in reply to Yogishwari Shanmukhappa
    TI__Genius 9260 points

    HI Yogishwari,

    Can you confirm what waveform is output of buffer and input in attached screenshot? This seems like a attenuated signal even if its on inputs or outputs. I would be able to help more if you can probe the input of buffer or PCIe clock and buffer output waveform. We should see a proper square wave with an output swing of 750mV single ended or 1500 mV measured with differential probe. 

    Best,

    Asim