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LMK05028: Behavior of phase Lock

Hideki Hayashi1
Expert 8880 points
Part Number: LMK05028


Hi team,

Undesired behaviors at PLL has found. Can you verify behaviors that customer seen is right or not?

1. When loss-of-phase lock, it seems that LMK05028 need to take more time than expected. (10 seconds for two periods) It looks like LMK05028 only do phase lock. Is it able that LMK05028 do frequency lock in order to lock faster?

2. Is there any limitation of frequency lock?

3. Regarding phase lock, it looks like too slow to do phase lock even if there are lots of periods. Is it able that LMK05028 phase lock faster when lots of periods, then lock slower within 90 degree?

Best regards,

Hideki

  • +1
    TI__Mastermind 34250 points

    Hideki-san,

    Since LMK05028 supports multiple configurations, the answers to your questions differ depending on several factors.

    • What is the DPLL reference input reference frequency, format, and duty cycle?
    • In what configuration is the device being used? (two-loop, three-loop, etc)
    • Is there a .tcs file for the configuration we can review? This is really crucial to us determining the root of the problem.

    Usually getting phase lock but not frequency lock indicates some issue with the DPLL validation parameters, or there may be something unique about the input such as gapped or missing pulses that prevents the frequency lock detect from validating properly. Phase lock is also a function of reference input frequency and DPLL loop bandwidth - lower loop bandwidth will increase lock time, and fewer TDC comparisons per second (especially for very low frequency input references) will greatly increase the lock time requirements. There is a fastlock function which uses a wider loop bandwidth initially to center the phase error, which can speed up lock time, but depending on the input reference frequency and TDC frequency it may not be useful.

    Regards,

    Derek Payne

  • 0 in reply to Derek Payne
    TI__Genius 12560 points

    Hi Hideki-san,

    Haven't heard on this very long time and assumed the issue got resolved.

    Closing the thread now. Feel free to open again or create new thread for further queries.

    Thanks!

    Regards,

    Ajeet Pal