I made three pcb boards with the PLL ADF4002 and an external VCO set to oscillate between 200 Mhz and 250 Mhz with a tuning voltage between 1V and 5V. I have a problem with one of these boards. It happen that sometimes it works well and randomly it gives a voltage around 2V in CP and it don´t change when I change the program to another frequency. I try to isolate the CP pin of the Low pass filter and have the same problem. Nevertheless even when the CP is set in 2V, I program the MUXOUT at Vdd or GND and it work well, so it´s not a program problem but I can´t explain why this happen because I have another board exactly the same and it work well every time.