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WEBENCH® Tools/LMK03328: Loop Filter Parameters

Kawai
Guru 19785 points

Part Number: LMK03328
Other Parts Discussed in Thread: PLLATINUMSIM-SW

Tool/software: WEBENCH® Design Tools

Hi Team,

Q1). Could you please tell us what the following parameters are and what is the target value for stable PLL opearation ?

- T3/T1 Ratio
- Gamma

Q2). What happens when used in bellow parameters ?

- T3/T1 Ratio = 0%
- Gamma = 19.46

Best Regards,

Kawai

  • 0
    TI__Expert 3482 points

    Kawai,

    You can find out their definition by clicking on the help button.

    There is a section that provides the description for each of the parameters. 

    I redirect your question whether to use gamma of 19.24 to product line. He/She will follow up with you.

     

  • 0 in reply to Alfred Chong
    Guru 19785 points

    Hello Alfred-san and Team,

    Thanks for your support.

    We will wait for your comments about LMK03328 operation used in the condition of gamma = 19.46, which the recommeded value is "0.24".

    The new information I found was that customer is using in 2nd order filter. Since WEBENCH simulation could not be run at "Filter Order = 2nd order", which we always have warning, customer and we are running simulation in 3rd order setting with C3=0pF.

    Is this the correct way to simulate 2nd order filter ?

    Best Regards,

    Kawai

  • 0 in reply to Kawai
    TI__Mastermind 28031 points

    Kawai,

    A third order filter with T3/T1 = 0 is really a second order filter.

    If you set C3 = 0 and the VCO input capacitance is zero, then this is a 2nd order filter.  Otherwise, the VCO capacitance could for another pole.  It might be better to set R3=C3=0 to ensure it is indeed 2nd order.

    As for the gamma value of 19 being away from the recommended value, what this means is this might take longer for the PLL to lock to frequency, but if this is a fixed frequency application, you might not care.

    Regards,

    Dean

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

    Thanks for your support. I have two more questions and a request.

    - Customer uses the device in fixed frequency, however, when at first system power up and LMK03328 to achive PLL lock, does gamma affect the lock time to be longer ?

    - Is there no affect to the PLL stability having the gamma value away from the recommendation ?

    - It would be helpful if WEBENCH could to run simulation correctly with "Filter Order = 2nd order" setting, since showing error.

    Best Regards,
    Kawai
  • 0 in reply to Kawai
    TI__Mastermind 28031 points
    Kawai,

    The gamma optimization parameter is discussed in great depth in my online PLL book "PLL Performance, SImulation, and Design" at ti.com\tool\pll_book.

    The clock architect is good for part selection and frequency planning, but the TI PLLatinum Sim tool at ti.com\tool\PLLATINUMSIM-SW
    It has a much more powerful design tool and shows the impact of the gamma optimzation parameter more fully. It doesn't support the LMK03328, but you can try a similar LMK device and change the charge pump gain and VCO gain and run the simulation


    Regards,
    Dean