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LMX2571: PLLutinum tool.

user4779049
Expert 2395 points

Part Number: LMX2571

Hi Team,

Please advises me on PLLutinum tool.
I tried to simulate LMK2571-EXT-VCO using this tool.
However, FDVI box was turned to be red.

Does it mean that FDIV can’t be implemented the value?
The configuration is as follow:
Ref = 26MHz
VCO freq = 470.125

Mita

  • 0
    TI__Expert 5370 points
    Dear Mita,


    thank you for your interest in LMX2571 and PLLatinum Sim. I have assigned your question to an engineer. Expect an answer before Monday the 28th of August.

    Regards, Simon.
  • 0
    TI__Mastermind 28031 points

    Mita,

    I'm not exactly which box you mean by "FDIV"

    If you are talking about the feedback "PLL_N" divider, there is minimum value.  With an external VCO frequency of 470.125 MHz, a 26 MHz phase detector frequency is too high as it will cause the minimum N divide to be too small.   Reduce the phase detector freqeuncy to 13 MHz and this will solve the issue.

    REgards,
    Dean

  • 0 in reply to Dean Banerjee
    Guru 19785 points
    Hi Dean-san,

    Where can we find the Minimum and Maximum spec for the Fractional N divider value in the datasheet ?

    Best Regards,
    Kawai
  • 0 in reply to Kawai
    TI__Guru** 119790 points
    Hi Kawai,
    Apology for not having specify the min. N value in the datasheet. In PLL mode, the min. N values are 4 and 8 for integer mode and 2nd order modulator respectively. However, you may find it works even if this requirement is violated. So, we have put a stringent warning threshold in PLL Sim so that people can aware of this.
  • 0 in reply to Noel Fung
    Guru 19785 points

    Hi Noel-san,

    Please find below divider setting. N divider setting seems to show warning in red when N divider is lower than 24. When Fvco = 630MHz, there is no more warning.

    Q1). What do you mean by "minimum N values 4 and 8" ?

    Q2) What happens when customer used with Fractional N divider = 18.xxxx ?

    Best Regards,

    Kawai

  • 0 in reply to Kawai
    TI__Mastermind 28031 points

    Kawai-san,

    1.  For the value in the red box,  PLLatinum Sim has 24 as the minimum value, but according to noel's statement, this value is OK.   But any case, ignore the red warning

    a.Integer Mode:   4

    b.  2nd Order Modulator:  8

    c.  1st Order Modulator:  4?

    d.  3rd and 4th order modulator? 

    2.  Based on Noel's statements, it seems like the fraction of 18.xxxx is fine

    3.  I am going to update the PLLatinum Sim tool to better reflect the correct numbers

    REgards,

    Dean