I am using the AD9552 evaluation board with an external 10 MHz reference. My problem is that when I turn on the board, it doesn't phase lock to the reference reliably. I have to cycle the power on the board several times to get it to phase lock. I've also found that I can get the board to phase lock by reducing the DC offset to zero and ramping it up to 1 V by hand. Switching the DC offset on and off does not seem to produce a phase-lock reliably.
I've added a DC bias of 1 V to the external reference with a bias tee. The peak to peak amplitude of the clock is 1.2 V.