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LMX2592: PLL can not lock.

Lian Wu
Genius 5250 points
Part Number: LMX2592

Dears:

Cusomer use  LMX2592 to generate 6000MHz output clock ,and the Reference clock is 200MHz.

The work mode of PPL is Integer, and the parameters is Vtune=0.090V, Fout=6048MHz.

But PLL can not lock.

Pls. kindly give some advice about it.

  • 0
    TI__Mastermind 28001 points
    Luck,
    C1 =0 may be problematic because the abrupt changes in the charge pump might cause issues. So at least put something there at least 22 pF or more.

    Now if it's not the filter, ther are many problems:
    1. Can you communicate with the device at all? Try software powerup/powerdown to verify.
    2. Is the VCO calibrating correctly? If so, it should be within 50 MHz of the proper frequency. There are 7 VCO cores of 183 different bands. To know the frequency range of the band you are in first do what you are doing to get the state you have (including programming FCAL_EN=1). Then try setting the VCO frequency to 1 GHz WITHOUT toggling FCAL_EN=1. This shows the lower end. Then try setting VCO frequency to 20 GHz WITHOUT toggling FCAL_EN=1 to find upper range. If VCO doesn't move, also check if loop filter is connected and not shorted to ground.

    Regards,
    Dean
  • 0 in reply to Dean Banerjee
    Prodigy 20 points
    Hi, it's me who asked help from Lian Wu. The reason why LMX2592 doesn't lock at 200MHz reference is PFD_DLY=2, which need to be set to 1. The device got locked after I set PFD_DLY=1.

    Thanks for your help.