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No output from ADF4350 when programmed correctly at certain frequencies

Hello,

I'm using the ADF4350 to generate the clock for the AD9914 and I would like the frequency to be either 2^31 Hz = 2147.483648 MHz or 3500 MHz which I generate from a 100 MHz reference. Using the evaluation software gives me the values I need to write to each register, shown below for the two frequencies. This works perfectly for 3500 MHz since MUXOUT - configured as  digital lock detect - goes high and the beatnote with another frequency source locked to the same reference is zero. However, when I program the ADF4350 with the configuration for 2^31 Hz, the digital lock detect never goes high. Has anyone else run into this issue before?

Thanks

  • It looks like the screenshot of the configuration for 3500 MHz wasn't included with my previous post so here it is

  • Hi,

    You are using 20 MHz PFD frequency for 3500 MHz and 160 kHz PFD frequency for 2^31 Hz. Your loop filter may not be appropriate for 160 kHz PFD operation. If you can send your loop filter, I can check it with ADISIMPLL. 

    Regards,

    Kudret

  • Thanks for your prompt reply. I tried your suggestion to operate them both at the same PFD frequency with the right loop filter, but now the lock is not working at either output frequency. I'm attaching a screenshot of of the two loop filters I used. The values in black are those suggested by ADIsimPLL for PFD frequency = 320 kHz, the values just below in red are the ones I am using in the new loop filter that runs at 320 kHz, and the ones in brown below those are for the first loop filter I tried where 3500 MHz was working. I am also attaching screenshots of the register data I write for both output frequencies.