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ADF4356 does not work at low temperatures

Question asked by Valimor on Dec 12, 2017

Greetings. In my project it is necessary to switch the synthesizer frequency in steps of 25 MHz in the frequency band 6300 - 6800 MHz in the temperature range from -40 to +50 degrees, and in the temperature range from +20 to +50 everything works fine, but at negative temperatures the PLL loop does not lock, or is locked only after a long warm-up (about 5 minutes), with a very narrow PLL loop (it looks like open-loop VCO). The increase in the loop current helps only partially, on the part of the frequencies the loop remains unstable. Any idea why this might happen?
By the way, the same situation was observed with the ADP5355 synthesizer, but after 2 minutes of warm-up the parameters stabilized and everything worked well.