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LMK05318: Output Setting

Kuan Wei Chen (Kevin Chen)
Genius 9710 points
Part Number: LMK05318

Dear Team,

A question, red rectangle is 156.25Mhz and Green rectangle is 25Mhz.

Does this acceptable for LMK05318?

BR

Kevin

  • 0
    TI__Mastermind 33790 points

    Hi Kevin,

    The crosstalk spurs between 156.25 MHz and 25 MHz (at multiples of 6.25 MHz) will be quite aggressive, see below. Ideally, outputs where the GCD frequency is in the jitter integration bandwidth should be separated as much as possible. I don't recommend placing 25 MHz next to 156.25 MHz unless the performance degradation on the 156.25 MHz output is acceptable.

    156.25 MHz with OUT4/5 disabled:

    156.25 MHz with OUT4/5 enabled:

    Regards,

  • 0 in reply to Derek Payne
    TI__Genius 9710 points

    Dear Payne,

    Thanks for the information.

    Out 0-3 are 156.25Mhz, with PLL1

    And 4-7 are 25Mhz, with PLL2

    It didn't improve the situation, right?

    Since the PLL2 have higher jitter

    BR

    Kevin

  • 0 in reply to Kuan Wei Chen (Kevin Chen)
    TI__Mastermind 33790 points

    Hi Kevin,

    Apologies for the delay. Placing 25 MHz on PLL2 does not improve the crosstalk, as the crosstalk is mostly seen at the output stages in the IC. And you are correct, PLL2 has a higher noise floor, so the 25 MHz signal jitter is worse with no change to the spurious behavior.

    Regards,