Re: Help!MY PLL!
Check obvious things, like are all dc voltages and grounds proper, is board layed out correctly, etc. If you put a DC voltage into the VCO tune port (always use a series 1 K resistor to avoid accidentaly blowing out the tuning varactor), does the VCO tune across your desired band, or does it stop oscillating at some input voltages.
Odds are good you are programming the PLL chip wrong. That chip does have a Mux Out pin. You can put in a precise synthesized RF signal for Ref, IF, or RF input, and look at the divided down output on the Mux Out with a precise counter. I like to run the test equipment synthesizer and counter off of the same 10 MHz source. You look at the Mux Out and figure out if the frequency on the counter is EXACTLY what you expect it to be. It is easy to be off by 1 bit, or to enter a not-allowed divisor ratio.
If all the dividers are being programmed properly, then I would suspect that my control loop filter is unstable. I would play around with some control loop simulation software to get more gain or phase margin, and see if it locks up. If you are not familiar with control loop filter, try using just a passive R-C loop filter which while not optimum should be more stable.
If it locks with a passive loop filter but not the active loop filter, either your control loop design is flakey, or there is something unstable in the op amp itself. Read the op amp data sheet carefully. Make sure the op amp layout is good (especially if it is a wide bandwidth op amp).