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LMX2820: Full assist, internal VCO external PFD mode

Taketo Sato
Genius 10325 points
Part Number: LMX2820
Other Parts Discussed in Thread: LMX2594,

Hello team,

Could you let me know a guidance of how to utilize full assist mode with internal VCO, external PFD mode?

First, I have to create look-up table by calibrating VCO with no assist or partial assist and readback the result of the VCO calibration.

In this phase, should I use internal PFD mode or external PFD mode?

I would like to know how to create look-up table for external PFD mode.

Best regards,

  • 0
    TI__Mastermind 28001 points

    Taketo-san,

    What I have done is use internal PFD mode to generate the table.  It might work with external PFD mode for table generation, but we have not tested this yet.


    Regards,
    Dean

  • 0 in reply to Dean Banerjee
    TI__Genius 10325 points

    Hello Dean-san,

    Thank you for the comment.

    Customer would like to know a way to Lock certainly in external PFD mode, and I think full assist mode is best way for the purpose so I asked the question.

    Can I think VCO status is uniquely determined by full assist setting and output correct frequency regardless of internal PFD mode or external PFD mode?

    If so, do you think if there are any other risk of unlock with internal VCO external PFD mode use case?

    Best regards,

  • 0 in reply to Taketo Sato
    TI__Guru** 107780 points

    Hi Sato-san,

    Yes, the calibration is irrelevant to the PFD mode.

    The locking mechanism is identical for all PFD modes, so far, we haven't discovered any issue with external PFD mode.

  • 0 in reply to Noel Fung
    TI__Genius 10325 points

    Hello Noel-san,

    Thank you for your comment.

    So, the way to generate a look-up table of LMX2820(internal VCO, external PFD) for full assist mode is same way what to do for LMX2594/5(internal VCO, internal PFD), and we can use the table for also external PFD mode. And with this way VCO will lock certainly, correct?

    Best regards,

  • 0 in reply to Taketo Sato
    TI__Guru** 107780 points

    Hi Sato-san,

    Yes, that is what I was told, we can do calibration in external PFD mode. With the calibration data, we can do full-assist frequency switching.