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LMK03000 - VCO frequency calibration

Kawai
Guru 19775 points
Other Parts Discussed in Thread: LMK03000

Hi Team,

Please tell me about the LMK03000 family frequency calibratoin.

Our customer will use 74.25MHz and 74.175MHz for OSCIN. OSCIN would be switched in the following 4 case.

  1) 74.25MHz --> 74.25MHz  (No calibration needed)
  2) 74.175MHz --> 74.175MHz  (No calibration needed)
  3) 74.25MHz --> 74.175MHz  (Need calibration ??)
  4) 74.175MHz --> 74.25 MHz  (Need calibration ??)

[Question]
Do you need to activate frequency calibration when OSCIN is changed from 74.25MHz to 74.175MHz or from 74.175MHz to 74.25MHz ?

* Customer is wondering if they could skip the calibration step as the frequency difference is not so much a big change between 74.25MHz and 74.175MHz. 

Best Regards,
Kawai
 

  • 0
    TI__Mastermind 32575 points

    Hi Kawai-san,

    The frequency calibration routine will automatically happen when the PLL divider ratio (specifically PLL N divider) is changed to achieve the frequency translation in 3) and 4), so it cannot be avoided.  Refer to the RECOMMENDED PROGRAMMING SEQUENCE in section 7.1.

    What is the customer's concern about having the frequency calibration step?

    Regards,
    Alan

  • 0 in reply to Alan O
    Guru 19775 points

    Hi Alan-san,

    I appoligize for my lack of information. LMK03000 will output the same frequency of OSCIN. In our customer's case, they will not change PLL dividers.

    In OSCIN transition case of  3) and 4), calibration will not happen unless you write to register R15.

    Our question was that whether one would need to activate calibration routine in this case or not.
    (Because the frequency different is small and there is no PLL divider change.)

    * In section 7 of the datasheet, there is a comment that any changes to the PLL R divider or OSCin requires calibration routine. So it seems you would need to re-program R15 when OSCin translation occur between 74.25MHz and 74.175MHz.

    Best Regards,
    Kawai

  • 0 in reply to Kawai
    TI__Mastermind 32575 points

    If there is no change to PLL divider and OSCIN freq change is small, you may bypass the calibration routine.

    Regards,

    Alan