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LMK00301: Output signal discontinuity

Lacey Lin
Intellectual 2900 points
Part Number: LMK00301


Hi team,

Below is the diagram of my customer's application.

The output signal of LMK00301 is LVPECL and the input signal of the CPLD is LVDS.

Customer use the CPLD to monitor the output clock of the LMK00301, and we found when the temperature is high, there occur the problem of frequency shift.

And we also get the input signal of the CPLD.

Could you help me to check the matching network between the LMK00301 and CPLD and give your comment to the problem.

Lacey

Thanks a lot

  • 0
    TI__Expert 8865 points
    Hi Lacey,
    Your request is assigned to responsible Apps Engineer and you will get an answer very soon.
    best regards
    Puneet
  • 0 in reply to Puneet Sareen
    TI__Genius 16845 points
    Hi Lacey,

    I recommend to replace the 33-ohm with 70-ohm resistors to reduce the swing to 325mV.

    What frequency shift do you observe? LMK00301 is a non-PLL based buffer. I do not expect the output frequency should not shift unless you observe the same frequency shift at the input.

    The problem with your CPLD input may be by an impedance mismatch. The impedance mismatch between the 100-ohm load and the clock trace is causing reflections which impact your signal integrity. There are several factors that affect signal integrity. You can simulate the signal integrity of the termination network using the LMK00301 IBIS model: www.ti.com/.../snam031

    Kind regards,
    Lane