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LMX2571: programming charge pump current

Thomas Noonan1
Prodigy 30 points
Part Number: LMX2571


I'm using the LMX2571 with an external VCXO and I'm a little confused by the Register  description in the data sheet for setting the charge pump current.  (R42 bits 0-4 and R41 bits 7-11)
The description shows:
0=Tristate
2=312.5 uA
4= 625 uA

...
30=3437.5 uA

If you increment by 312.5 uA you reach 3437.5 uA at a register value of 22.  Should the max current be 4687.5 uA or are there additional states not shown.  Also these increment values are not what i find in the Kpd pull down menu on PLLatinum Sim.  I find a similar issue with the charge pump setting for the internal VCO.

Thanks,

Tom

  • 0
    TI__Mastermind 28590 points

    Hello Tom,

    This is the full decode.  So as you suspected, there are intermediate values, note setting 16.  This values come from the TICS Pro GUI software for programming the LMX2571.

       * I will note the need for updating the datasheet.

    Thanks for your feedback.

    0 = Tri-state
    1 = Reserved
    2 = 312.5 uA
    3 = Reserved
    4 = 625 uA
    5 = Reserved
    6 = 937.5 uA
    7 = Reserved
    8 = 1250 uA
    9 = Reserved
    10 = 1562.5 uA
    11 = Reserved
    12 = 1875 uA
    13 = Reserved
    14 = 2187.5 uA
    15 = Reserved
    16 = 1250 uA
    17 = Reserved
    18 = 1562.5 uA
    19 = Reserved
    20 = 1875 uA
    21 = Reserved
    22 = 2187.5 uA
    23 = Reserved
    24 = 2500 uA
    25 = Reserved
    26 = 2812.5 uA
    27 = Reserved
    28 = 3125 uA
    29 = Reserved
    30 = 3437.5 uA
    31 = Reserved

    Here is the decode for the internal CP, it is the same as above, except has the odd values filled in.

    0=Tri-state
    1=156.25 uA
    2=312.5 uA
    3=468.8 uA
    4=625 uA
    5=781.3 uA
    6=937.5 uA
    7=1093.8 uA
    8=1250 uA
    9=1406.3 uA
    10=1562.5 uA
    11=1718.8 uA
    12=1875 uA
    13=2031.3 uA
    14=2187.5 uA
    15=2343.8 uA
    16=1250 uA
    17=1406.3 uA
    18=1562.5 uA
    19=1718.8 uA
    20=1875 uA
    21=2031.3 uA
    22=2187.5 uA
    23=2343.8 uA
    24=2500 uA
    25=2656.3 uA
    26=2812.5 uA
    27=2968.8 uA
    28=3125 uA
    29=3281.3 uA
    30=3437.5 uA
    31=3593.8 uA

    73,
    Timothy