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LTC6952 Last Time Buy
The LTC6952 is a high performance, ultralow jitter, JESD204B/C clock generation and distribution IC. It includes a Phase Locked Loop (PLL) core, consisting...
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LTC6952 on Analog.com

LTC6953 Last Time Buy
The LTC6953 is a high performance, ultralow jitter, JESD204B/C clock distribution IC. The LTC6953’s eleven outputs can be configured as up to five JESD204B...
Datasheet
LTC6953 on Analog.com

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LTC6952 controller with LTC6953 followers EZSync multi-chip sync issues

		
	
				

			

									
					    ACoffman
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jan 30, 2020 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    Good Afternoon,
    

    I am currently working with a multi-chip synchronization architecture with one (1) LTC6952 as my controller feeding two (2) LTC6953s as my followers. I am trying to verify the synchronization is functioning as I would expect with the DC2609A and DC2610A and am running into a few issues with consistency.
    

    I have provided a simple block diagram of my setup below for reference:
    

     
    

    Ref CLK: 100MHz onboard Crystek oscillator
    

    Green Trace: AC coupled single ended 4GHz clock output from LTC6952 to Ref CLK input to LTC6953
    

    Purple Trace: DC coupled, 100 Ohm terminated 500MHz clock output from LTC6952 to EZSync inputs on LTC6953
    

    Black Trace: AC coupled 4GHz output clock from LTC6953
    

    Red Trace: AC coupled 500MHz SYSREF output from LTC6953
    

    

    NOTE: All clock outputs from LTC6952/LTC6953 are set to divide by 1. All SYSREF outputs from LTC6852/LTC6953 are set to divide by 8.
    

    

    What I am currently seeing is a consistent 1 clock cycle skew between SYSREF outputs between my two boards. I can not seem to get the SYSREFs to align on the same clock edge no matter what I try with the evaluation boards. The GUI itself does not offer much confidence that the changes being made are actually being enacted on the device, so that could be part of my problem. In general I have a few questions regarding this setup however that I am hoping someone can help resolve.
    

     
    

    Yellow Trace: CLK output from LTC6953 #1
    

    Green Trace: SYSREF output from LTC6953 #1
    

    Orange Trace: CLK output from LTC6953 #2
    

    Blue Trace: SYSREF output from LTC6953 #2
    

    

    Questions:
    

    1. Is this a valid setup? I see the reverse mentioned several times, but never a 52 feeding 53s.
    

    2. Why do my SYSREF signals transition on the rising edge of the clock output and not the falling?
    

    3. The LTC6953 datasheet page 20 mentions "For all cases of EZSync synchronization, the CONTROLLER must be programmed to output seven pre-pulses to each FOLLOWER before the   FOLLOWER outputs or any follower-synchronous CONTROLLER outputs start clocking." Is this possible with the LTC6952 without doing a pure pass through from a logic device? If no, am I expected to use a logic device to accomplish this?
    

    4. The LTC6953 datasheet page 16 mentions "The EZS_SRQ input state or SSRQ bit must remain high for a minimum of 1ms.". How is this intended to be accomplished with my current setup? With a 4GHz VCO frequency this does not seem achievable with a max divide ratio of 4096 on the outputs. I presume the digital sync is not deterministic, but I hope the EZSync inputs can be for repeat behavior.
    

    5. Using the GUI the synchronization routine is not very clear. I see in the LTC6952 datasheet there is a programming and sync guide (shown below), but I have to be very careful how I program these devices as often I will not get any response from SYSREF outputs if the sync is not performed correctly. Do you have a recommendation for how to synchronize my setup?
    

    

    LTC6952 Datasheet page 74
    

     
    

    

    I would like to be able to power cycle these boards and easily repeat this exercise of synchronization but I am not able to do this at the moment. Any feedback that can be offered would be greatly appreciated. If there are any questions about what I have mentioned I would be happy to answer them.
    

    

    Regards,
    

    Aaron
    

    
			
    
			
									
		                             
                        

    
    
                                            
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jan 30, 2020 11:07 PM
            
            
						
			            		
      
		
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      Hi Aaron,
      

      Thanks for all the information.  It looks to me like you are trying to do an EZSync (Clock Distribution) as shown on page 73 of the LTC6952 datasheet, but referenced the ParallelSync (Reference Distribution) on page 74 of the LTC6952 datasheet.  There is a lot of information to digest in that digest.   
      

      Probably the most important hardware setup thing to be aware for EZSync is all the connections between the boards require DC coupling.  All the caps on the DC2609 Outputs should be removed and all the caps on the DC2610 inputs should be removed   & replaced with the correct component (in most cases a 0 ohm resistor).  All connections should be differential and terminated correctly, as shown on page 73.  I think after you do this, everything else will fall into place.
      

      The other thing I'd like to point out, is we have provided the LTC6952Wizard set files for these application examples in the datasheet.  For page 73, you can use these files denoted by the red arrows.  From the LTC6952Wizard menu, select File --> Load Settings to find these set files.
      

      As a side note, we have the DC2430 https://www.analog.com/media/en/dsp-documentation/evaluation-kit-manuals/DC2430AF.PDF.  Which allows you to program one Linduino (Arduino environemnt) and talk to several boards.  This board was designed specifically for these multi-clock applications.   You can use this one GUI and manually turn the switch to connecto the next board.  After that, you can program Arduino to program all three parts, and automatically switch between boards.   I think I may still have the Arduino code laying around somewhere for the automated version of  page 73 example. 
      

      I'll look at the rest of your questions tomorrow.
      

      

       
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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