AD9525 ignores REFA

HI

When configuring a clock for my AD9914 i ran into a problem with my AD9525 chip. It works, i can set and read the registers, but it ignores the REFA input. Output is visible but not the frequency i expect (3.4GHZ instead of 3.5 as configured). The PLL is shown as "not locked". My code is:

    ad9525_send(0, 0b10000001); // MSB FIRST, NO STREAMING, SDO active
   ad9525_send(0x232, 0x01); //ioupdate


//25MHz Ref: M=1, B=28, P=5, R=1
    ad9525_send(0x004, 1); //reads back active registers
    ad9525_send(0x010, 0b00001111); //Charge pump
    ad9525_send(0x013, 0b11011101); //B divider
    ad9525_send(0x1e0, 0b00000000); //M divider


    ad9525_send(0x017, 0b11100011); //CP und RefA-clock (dyn) ----no Clock visible!--------
    ad9525_send(0x018, 0b00010001); //REF_MON pin: RefA inv ----doesnt work either------
    ad9525_send(0x019, 0b00001100); //255 PFD cycles to lock, high range lock window, normal lock detect operation
    ad9525_send(0x01a, 0b11110000); //Monitors und Switchover
    ad9525_send(0x01c, 0b00101010); // N divider on REFA on, REFB off

    ad9525_send(0x0f0, 0b00000111); // Ch0 LVPECL

    ad9525_send(0x232, 0x01); //ioupdate

Hardware is wired correct, 25 MHz arrive at the chip, i measured at its pins. Can anyone see an error in my code?? Did i miss a divider or something else?

  • 0
    •  Analog Employees 
    on Mar 22, 2017 6:40 PM over 3 years ago

    Hello Redstone,

    I input your settings into the eval software, and found that you had the charge pump held static at Vcp/2. I also noticed that the feedback divider was set to 28, which would be correct for a 350 MHz VCO. I fixed it by choosing an R divider of 1 (instead of 2) and making the feedback divider 140. I hope your loop filter is still stable with 2x the loop gain.

    Also, we don't normally vary the anti-backlash pulse unless we really need to.  If this doesn't work, let me know what the reference monitor is indicating about the status of the input.

    -Paul

    The exact text in between the horizontal equal signs is what's in the eval software .STP file:

    =======================

    <header>
    product = AD9525
    softwareversion = 1.0.0.2
    </header>

    <registers>
    Register (Hex),    Value (Hex),    Value (Dec)
    0x0,        0x00,        0
    0x2,        0x00,        0
    0x3,        0x00,        0
    0x4,        0x00,        0
    0x10,        0x0D,        13
    0x11,        0x00,        0
    0x12,        0x00,        0
    0x13,        0xDD,        221
    0x14,        0x0C,        12
    0x15,        0x00,        0
    0x16,        0x00,        0
    0x17,        0x2D,        45
    0x18,        0x17,        23
    0x19,        0x0C,        12
    0x1a,        0xD0,        208
    0x1b,        0x00,        0
    0x1c,        0x0A,        10
    0x1d,        0x00,        0
    0x1e,        0x00,        0
    0x1f,        0x00,        0
    0xf0,        0x00,        0
    0xf1,        0x07,        7
    0xf2,        0x04,        4
    0xf3,        0x04,        4
    0xf4,        0x04,        4
    0xf5,        0x04,        4
    0xf6,        0x04,        4
    0xf7,        0x04,        4
    0xf8,        0x10,        16
    0xf9,        0x00,        0
    0xfa,        0x00,        0
    0x190,        0x00,        0
    0x191,        0x00,        0
    0x192,        0x00,        0
    0x1e0,        0x00,        0
    0x1e1,        0x00,        0
    0x230,        0x00,        0
    0x231,        0x00,        0
    0x232,        0x01,        1
    </registers>

    <frequencies>
    25000000;0;0
    </frequencies>

    ==========================================

  • HI

    Thanks for your quick answer! Too bad this eval software doesn't work without the eval board (which i dont have).

    To hold the charge pump steady was the only way to get a output signal somewhere near the 3.5GHz. Good for checking the voltage and ensuring the proper work of the VCO.

    Yes, for 25MHz Ref the dividers should be M=1, B=28, P=5, R=1. Seems like i missed to disable the R-divider.

    I will try out this config soon, maybe somthing else went wrong, too.

  • 0
    •  Analog Employees 
    on Mar 27, 2017 4:28 PM over 3 years ago

    Dear Redstone,

    The eval software works fine without the eval board. It's how I checked the settings.

    -Paul

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:46 PM over 2 years ago
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin