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LMX2582: LBW

HuTer
Prodigy 120 points
Part Number: LMX2582

Hello,

I'm using LMX2582 and I need to calculate the loop bandwidth.

How can I know the equations used by PLLatinum Sim to calculate the LBW? I referred to  "PLL Performance, Simulation, and Design © 2017" Page 378 to calculate the open-loop and then the closed loop cutoff frequency, it differs from the one appeared in the PLLatinum Sim. I considered the Type of the filter used, Gain, R&C Values, input & output Frequencies, Kvco, CPGain, N...

Regards,

  • 0
    TI__Guru* 81490 points

    Hi Hu,

    I would say the result from PLL Sim is rather accurate because we have considered the actual VCO and PLL characteristics. You can rely on the PLL Sim result.

    In addition, if you select "Advanced" mode, you will see more options and design strategy.

  • 0 in reply to Noel Fung
    Prodigy 120 points

    Hi Noel,
    Thank you for your fast response, indeed I'm searching for the equations used in calculating the Loop BW provided by PLLatinum.
    Moreover, the value of KVCO,  for a given Fvco, differs between the one appears in PLLanium and TICsPRO.
    Anyway, thanks for your help.



  • 0 in reply to HuTer
    TI__Guru* 81490 points
    Hi Hu,

    PLL Sim is a free tool for the public, I am afraid we have no plan to disclose the equations being used.
    For the Kvco question, I see you have another post on it. That post will be answered by our colleague, who built the library for these tools.
  • 0 in reply to Noel Fung
    TI__Mastermind 27581 points

    Hu,

    Comparing the Datasheet, TICSPro, and PLLatinum Sim, the results are very similar, but PLLatinum Sim is slightly different.  Also below is the TICSPro code.  What it does is use a linear approximation between each of the known values in the datasheet.

    PLLatinum Sim uses more complete data and slightly more accurate, but they all are fairly close.

    def UpdateVCOGain():
    Fvco=Fvco_FREQ.dValue

    if (Fvco<3550):
    Kvco = 27.4
    elif (Fvco<4200):
    Kvco = 28+(30-28)*(Fvco-3700)/(4200-3700)
    elif (Fvco<4700):
    Kvco = 30+(33-30)*(Fvco-4200)/(4700-4200)
    elif (Fvco<5200):
    Kvco = 33+(36-33)*(Fvco-4700)/(5200-4700)
    elif (Fvco<5700):
    Kvco = 36+(41-36)*(Fvco-5200)/(5700-5200)
    elif (Fvco<6200):
    Kvco = 41+(47-41)*(Fvco-5700)/(6200-5700)
    elif (Fvco<7100):
    Kvco = 47+(51-47)*(Fvco-6200)/(6800-6200)
    else:
    Kvco = 53
    CalculatedKvco.dValue=Kvco

    Compare results from different tools:

    Fvco Core Datasheet PLLatinum Sim TICSPro
    3700 VCO1 28 25.8 28
    4200 VCO2 30 29.8 30
    4700 VCO3 33 32.1 33
    5200 VCO4 36 35.3 36
    5700 VCO5 41 40.2 41
    6200 VCO6 47 44.7 47
    6800 VCO7 51 51.9 51

    REgards,
    Dean

  • 0 in reply to Dean Banerjee
    TI__Guru* 81490 points
    Dean's answer was regarding another post.
    I will close this post and paste his answer to the correct post.