ADF4356 cold start unlock

Hello,

I am currently evaluating the EVAL-ADF4356 board.
When I power up the evaluation board at room temperature and execute "Write Init. Seq", the output waveform is normal and the PLL indicates Lock.

However, when I power up the board in a –15°C environment and perform "Write Init. Seq", the output waveform shows increased noise and the PLL becomes unlocked.
During this test, the PC controlling the evaluation board remains at room temperature.

To suppress this issue, I manually wrote the VCOCORE, band, and bias values that were read at room temperature, and this completely resolved the problem.
From this observation, I suspect that VCO band selection is not functioning correctly at low temperatures.
Even when I set VCO Band Div = 255 and ADC Clock = 255 in the evaluation board GUI, the frequency of occurrence decreased but the problem was not fully resolved.

Could you please advise if there are any other possible countermeasures or settings I could try?

• The setup consists of the evaluation board connected to a PC using the GUI.

• The PFD frequency is below 75 MHz.

• I have already checked and tried the suggestions from the following discussions, but they did not resolve the issue:

  • https://ez.analog.com/rf/f/q-a/121085/adf4356-unlock-during-startup

  • https://ez.analog.com/rf/f/q-a/598038/adf4356-lock-problems

  • https://ez.analog.com/rf/f/q-a/98588/adf4356-fails-to-lock-to-2-4-ghz-and-settles-at-2-38-ghz

I also have ADIsimPLL and GUI configuration data available, but since they contain proprietary information, I cannot share them in an open community.

Thank you very much for your support and advice.

Best regards