I am using both the ADF4356 and the ADF4002 in a project. My issue is that on the '4356, I am unable to program MUXOUT to produce any response. 35mV all the time. This is true on multiple of our PCB prototypes. The MUXOUT pin only drives a CMOS buffer... not much of a load. I can open that path and there is no change in behavior.
The ADF4002 MUXOUT, however, works just fine... under program control it shows Lock status and can flip between Dvdd and DGND.
The ADF4356 PLL locks OK at 4.7GHz (Vtune is a reasonable value.. and not railed). So our SPI register writes must work.
I can toggle its REG4 between 0x8008984 and 0x10008984... which should produce Dvdd and DGND transitions on MUXOUT. This works on the ADI demo board. I checked all the IC's power supply pins, they are all correct.
I thought the lack of response might be due to register Double Buffering, but the Demo board uses single writes to REG4.
I added a 10K pullup to 3.3V, thinking that when MUXOUT is set to DGND, I might see a response. The node is pulls up to 3.3V as if the pin is tri-stated. I then flipped the DB8 level select to 1.8V. Hmmm, now the pin pulls up to 2.5V.
