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LMK05318B: Is it possible to generate 8 outputs in APLL only mode

Part Number: LMK05318B

Hi Experts,

I want to operate LMK05318B in APLL-Only mode: feed reference clk through XO input, and generate 8 outputs from VCO1. DPLL and APLL2 are not used. However, datasheet says OUT7 is muted if DPLL is unused and no reference clk input. I want to know is it possible to disable this function and make OUT7 can also generate outputs from VCO1?

Thank you!

John

  • Hi John,

    I looked through the datasheet and did not see a general statement of OUT7 being muted if the DPLL is unused. Section 9.3.16 says something similar, but that section is specifically about zero-delay synchronization for 1-PPS I/O. OUT7 is special because I think it is the only output that supports 1-PPS outputs, and in ZDM if there is no reference it does not really make sense to create an output. In normal operating conditions, OUT7 should act like the other outputs and you should be able to source from APLL1 if the DPLL and APLL2 are unused and disabled.

    Best,

    Evan Su

  • Hi Evan,

    The datasheet says "When the DPLL is not locked and the DPLL reference input is invalid, the OUT7 clock is held in mute state (no
    clock)". Customer's use case is feed 10MHz reference into XO input and lock VCO1 to this input and generate 100MHz output. I have tried for long it seems OUT7 is always in mute condition. Here i attached the configuration i used, you can try it.

    Thank youi!

    JohnLMK05318BEVMCofig_10M in_100M APLL1out0to7.tcs

  • Hi John,

    I took a look at your configuration and have a few ideas that you could try to ensure that all of the DPLL and ZDM features are off:

    • In the starting "Wizard" page it doesn't seem like the DPLL system was disabled 
      • You can disable it and continue through the rest of the Wizard regenerate the configuration
    • In the "APLL1" page, the mode is set to DPLL mode
      • If the Wizard has not fixed it already, change it from DPLL mode to Free-run mode 
    • In the "Outputs" page, the CH7_SYNC_EN checkbox is turned on:
      • Uncheck it, I think this is related to the ZDM system.

    Let us know how it goes, if it still does not work I can contact a device expert.

    Thanks,

    Evan Su

  • Hi Evan,

    Thank you! 

    I did not find the options to disable DPLL in Wizard pages, pls let me know how to do it.

    I did have selected PLL Mode as, 'Free-run mode' in 'Advanced/APLL1' page. Please check the configuration 'LMK05318BEVMCofig_10M in_100M APLL1out0to7.tcs' I sent last time.

    Yes in the 'Outputs' page the CH7_SYNC_EN checkbox was checked. I will have customer uncheck it and feedback the result to you. While I do not think it works. As my understanding it is just used to sync the output divider.

    Regards,

    John

  • Hi John,

    I did not find the options to disable DPLL in Wizard pages, pls let me know how to do it.

    Click on the "Wizard" title and the setting should be there. Right now the DPLL is not doing anything, but I think disabling it in software should shut down the circuits and save some power.

    I did have selected PLL Mode as, 'Free-run mode' in 'Advanced/APLL1' page. Please check the configuration

    I reloaded your configuration today and it says Free-run mode, I must have made a mistake yesterday. My apologies.

    I will have customer uncheck it and feedback the result to you. While I do not think it works. As my understanding it is just used to sync the output divider.

    Thanks. My logic is that the behavior of muting OUT7 when there is no reference happens when ZDM is enabled. The datasheet says that ZDM is enabled by two register settings: 

    So we should uncheck the OUT7 SYNC checkbox. I noticed today that on the "Advanced" --> "DCO, ZDM and Misc" page, there is another checkbox we need to clear:

    Please ask the customer to fix that as well. With these two changes ZDM should be completely off and I hope that the output would be unmuted.

    Best,

    Evan Su

  • Thank you Evan, yes this should work. Previously I always ignored Wizard page and directly went to Wizard/Set XO page for configuration so did not find this configurations.

    Regards,

    John

  • Hi Evan,

    Yes, finally OUT7 output is enabled once DPLL is disabled. Thank you for your help.

    Regards,

    John

  • Hi John,

    Happy to hear that OUT7 is working again. I still recommend that the customer turn off ZDM if they have not already, but with the DPLL disabled it should not do anything. Maybe the ZDM circuits are integrated into the DPLL anyway. Let us know if you have any more questions in the future.

    Best,

    Evan Su