I am using your ADF4159 on your evaluation board EV-ADF4159EBxZ Rev E with an off board VCO. When monitoring the muxout, set to digital lock detect, it seems that at whatever frequency I set the PLL, the lock detect line always indicates lock except for a short duration low pulse, presumably as the PLL changes frequency. It seems to indicate lock even when obviously not in lock, for example if I set the desired output frequency many GHz below or above the capabilities of the VCO, it still pulses low then stays high. Monitoring the output frequency of the VCO confirms that it is not in lock. The only way it seems to unlock is when I remove the reference source.
Is this to be expected? Is there anything I can do to improve the situation? We need a reliable lock indicator, preferably without having to access the LOL bit L1 of function register R3.
I assume that it is to be expected that the on-board muxout LED does not illuminate since the output voltage and drive capability of the muxout line is too low?