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LMX2595: FCAL_EN bit for Lock Detect - FULL Assist Mode

Dylan g
Prodigy 170 points
Part Number: LMX2595

I am using the LMX2595 in Full Assist mode, with all the relevant force bits set high and everything

I've noticed that the MUXOUT signal only goes high for Lock Detect when the FCAL_EN bit is asserted, is this normal and necessary for the lock detect to work in Full Assist mode?

EDIT: Conversely, I can not seem to get the lock detect bit to go high when it is in full assist mode without that FCAL_EN bit asserted.

  • 0
    TI__Genius 12560 points

    Hi Dylan,

    In full assist mode, you don't need to disable FCAL, you can keep FCAL_EN=1.
    Lock detect will check for VCOcal complete as well as Vtune, if both of these factors meet the threshold, LD will turn HIGH.
    When FCAL_EN=0, VCOcal will be 0 and therefore LD will always LOW.

    Thanks!

    Regards,

    Ajeet Pal

  • 0 in reply to Ajeet Pal
    Prodigy 170 points

    Oh perfect, ok I was thinking I was doing something wrong then

    As a follow up, what circumstances does the LD go low in Full Assist? Is it just when moving VCO Cores, or do the switching caps/numerator/n divider also play a role? Right now it isn't going low meaning it's always locked (allegedly), but I presume that has something to do with me staying in the same VCO core

  • 0 in reply to Dylan g
    TI__Genius 12560 points

    Hi Dylan,

    In full assist mode after VCOcal with FCAL_EN=1, LD always will high, i.e. PLL locked. LD can be low, if there is an incorrect VCO core and/or capcode / Num are selected.

    Regards,

    Ajeet Pal

  • 0 in reply to Ajeet Pal
    Prodigy 170 points

    Hi Ajeet,

    I believe I have solved my problem. My LD was set to VCOcal, but it turns out the LD type I want is indirect Vtune, which will let me know when my output is locked. Just took programming R59 to 0x0001 to fix that. Am I correct in my thinking for the Vtune voltage correlating with the locked output?

  • +1 in reply to Dylan g
    TI__Genius 12560 points

    Hi Dylan,

    Yes, your understanding is correct. LD_Type shows the status of VCO cal only or VCO cal + Vtune. While keeping LD_Type -->1, it will look for both threshold and turns on the LED once PLL is locked.

    Regards,

    Ajeet Pal