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LMX2594: Datasheet phase noise plots Figure 6 - Figure 11: Charge Pump settings

Stuart Rumley
Prodigy 250 points
Part Number: LMX2594

The LMX2594 datasheet phase noise plots figures 6 through figures 11.  What is the charge pump setting for these plots?

  • 0
    TI__Mastermind 28011 points

    Maximum charge pump setting of 15 mA.

    Regards,

    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 250 points
    Just to be clear, you are saying that these PN plots in the data sheet were taken when the CP was at its maximum value of 15mA? And can I assume that the optimum PN performance will always be achieved when the CP is at maximum?
    Thank you.
  • 0 in reply to Stuart Rumley
    TI__Mastermind 28011 points

    Best PLL noise happens at the highest charge pump gain.

    For some devices, the PLL figure of merit and the PLL flicker noise degrade for lower charge pump currents.  But for other devices, there is no degradation.

    This all depends on what dominates the PLL noise.  If it is dominated by the charge pump, then typically it is more impacted by the charge pump gain.  But if it is dominated more by the dividers, then not so much.

    In the case of the LMX2594, the change in the PLL noise for lower charge pump currents is neglible, so the lower charge pump gain is as good (or at least within 1 dB0 as the highest one.

    Regards,

    Dean