I have a modular based ADF4350. In my design ,the power supply is +3.3V, the maximum frequency is near to upper frequency limit of adf4350.In design period, the condition of modular is very well, in different test, including +85℃，+25℃，-40℃，and heat run. For some reason, the Vtune can’t be measured.
After three years, the signal can’t locked at +85℃. The signal can be locked at +25℃, the Vtune is +3.05V. So we adjust the power supply from +3.3V to +3.6V, the signal can be locked at +85℃, the Vtune is +3.20V.
Tens of modular are tested, there is some variation of Vtune in different conditions, but the variation will not exceed 0.4V. In tests , small part of chip’s Vtune is 2.5V at maximum frequency.
So I have some questions:
1. Will the value of Vtune be charged along the time? Will it be stable after some time?
2. The phenomenon of the test in individual case or all case?