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AD9525 ignores REFA

Question asked by RedstoneTTL on Mar 21, 2017
Latest reply on Mar 27, 2017 by pkern

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?

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