LMX2820: phase is not deterministic after giving SYNC pulse continuously

Hi Noel, 

Thanks for your reply.

I tried that way only but it is NOT phase synchronized / deterministic when VCO is in full assist calibration. On the other hand when VCO is in NO Assist calibration then phase is synchronized as it is there in App note you suggested (I observed these two scenario's in my lab) 

In your Lab, Can you please try phase synchronization when LMXs VCO is in full assist calibration and let me know 

Hi Rajani,

Did you mean instant calibration?

Usually we say no assist = full assist. That means we will do an auto-calibration for every frequency point of interest and then apply the VCO data manually. 

Instant calibration is an upgraded version of full assist. It will do the auto-calibration at some discrete frequency points and apply the VCO data automatically.

Hi Noel, 

I am not doing instant Calibration. I applied VCO data manually (RF out:354MHz)

Hi Rajani,

Did you program FCAL_EN bit back to =1 before sync?

Category 2 and 3 SYNC:
• Synchronization requires register FCAL_EN = 1. Before feeding the SYNC signal to LMX2820, program
register R0 with FCAL_EN = 1.

Yes Noel i did FCAL_EN=1. 

Hi Rajani,

I just tried with my board (OSCin=fpd=100MHz), I don't see an issue.

I program each synthesizer with RESET=1, then RESET=0, then load all registers (full assist, FCAL_EN=0), fout = 354MHz.

Then I program R0 (FCAL_EN=1) to each synthesizer, and then provide a sync pulse from LMK04832, the synthesizers sync together. 

Thanks a lot  Noel For Testing in your lab.

I will contact you separately if i won't figure out the issue with our Eval boards