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AD9518-1 - Script with registers settings

Dear supported

My customer is using the AD9518-1.


Required Fout= 122.88Mhz on out4 (780mv) . The external Reference clk on REF1 is 25Mhz.


Currently it seems like the PLL is not working,


  1. 1.      We get ~1.2Ghz from VCO + clocks on output0-5 depending on the dividers.
  2. 2.      We can’t control the PLL by changing P, R, A, B dividers parameters
  3. 3.      Turning the PLL on/Off (reg 0x10 = bits[1:0] =  2’b11/2’b00 . makes no change on output frequency.


Please advise.

Any scipt or registers settings file available?





  • Dear Freddy,

    I assume you want 122.88 MHz, but the schematic above shows Fout=125 MHz. You can't get 125 and 122.88 out at the same time. Let's assume you want to reconfigure the part for 122.88 MHz out.

    The first step in working with the AD9518-1 is to design the loop filter using ADIsimCLK. It appears that you've done this already, but in case you haven't, this page has a link to downloading it:

    In fact, this page has just about everything you need to work with the AD9518-1.

    The next step is downloading the eval software and following UG-075, both of which can be found on the above link.

    For 25 MHz in, 122.88 MHz out, I recommend:


    N div =12288 (P=16, A=0, B=768)

    VCO div = 5

    Channel divider = 4

    Icp = 3.6 mA

    If you refer to Table 3 in UG=075, you'll see a loop filter design that will work for this application. You may be able to use the same loop filter as you show above, but I can't quite read the component values.

    Next, you can use the evaluation software to program the part, and you should get register settings like this:

    (Be sure to turn on the PLL, and enable the reference input. (The user's guide explains how to do this.)

    When programming the part, it's critical that you perform the VCO calibration step at the end of this script when there is a valid reference input applied, or the part won't lock. Here are the settings that will program the part as you see in the above picture:

    Reg addr, Reg value (binary), Reg value (hex):























































    VCO Calibration step:





    -Paul Kern