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Original question:

LMX2571: LMX2571 MULT divider

LMX2571: VCO calibration

Kai Nomiyama
Expert 5755 points

Part Number: LMX2571

Hi Team,

I have a question about VCO calibration.
Datasheet describes typical VCO calibration time is 140us.

Question here is it allowed to re-send new frequency data before calibration is done?
Wehn it's allowed, does new frequency data become valid?

e.g)
send F1 data to LMX2571 then do calibration(FCAL_EN=1). → before 140us has passed, send new F2 data to LMX2571 then do calibration(FCAL_EN=1).

Regards,
Kai

  • 0
    TI__Genius 9920 points

    You are right.

    All dividers setting in PLL should be ready before calibration.

    If the N-divider is changing, program the relevant registers, then program R0 with FCAL_EN = 1.

  • 0 in reply to Shawn Han
    TI__Expert 5755 points

    Hi Han,

    Thank you for your reply.

    We do calibration when we change divider value but question here is when we change divider value before calibration has been done, there is no problem?

    here is procedure
    1. send F1 divider data to LMX2571
    2. do calibration (program R0 with FCAL_EN = 1)
    3. before F1 calibration is done(<140us), send F2 divider data to LMX2571
    4. in such case(F1 calibration is not finished but new F2 data is sent to LMX2571), there is any problem?


    Regards,
    Kai

  • 0 in reply to Kai Nomiyama
    TI__Genius 9920 points

    This operation can't achieve the calibration result for F2, so you need one more calibration after F2 data.

  • 0 in reply to Shawn Han
    TI__Guru** 121600 points

    Hi Kai,

    The divider is outside the loop, any change in divider does not need a VCO calibration. 

    VCO calibration is required only if its frequency is required to be alternated.

    So, in your procedure, step 2 is not necessary. 

    In cases when F1 calibration is in progress, you can program F2 registers without any conflict because F2 is not active. You can also program F1 non-PLL loop registers such as output power setting and channel divider setting.