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AD75019 Production
The AD75019 contains 256 analog switches in a 16 × 16 array. Any of the X or Y pins may serve as an input or output. Any or all of the X terminals may...
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AD75019 on Analog.com

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AD75019 ICs work consistently as expected at 4Mhz but inconsistently at lower frequencies.



		

			

									
					    newEngineer
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Apr 12, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    AD75019 IC , The VCC is +12V, VSS = -12V , VDD = +5V, DGND = 0V, 
    

    Pclk , Sclk and Sin are driven from an FPGA . There is a voltage translator which converts the FPGA signals at 3.3V to 5V signals.
    

    We have been using this IC in our project for several years now, with the same configuration and have been running the control signals at 2Mhz. 
    

    In the latest set of PCBs that we got from the manufacturer, We saw that the ICs didn't work consistently at 2Mhz. By this I mean, 1 out 100 times all the Switches would turn on on one IC and none of the switches would turn on on another IC. I verified that the protocol and bit selection is correct. The signal looks unchanged when the switches configure correctly vs when they dont.
    

    Suspecting timing issues I reduced the clock frequency to 1Mhz. The inconsistency was more pronounced now. It failed to configure correct on every other run.
    

    I increased the frequency to 4Mhz and the inconsistency went away. 
    

    The rise time remains unchanged at apprx 2ns with varying frequency.. I have attached the scope traces at 1Mhz.  Please advice on what might be cause of this issue? 
    

    In the scope trace, blue is SIN, Green is SCLK, yellow is Pclk, purple is DGND, Pink is VCC
    

      
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                        
                on Apr 13, 2022 10:27 AM
            
            
					
      
	
      

		
		
      
					
      Hi newEngineer, 
      

      This is a strange one.  I am not sure what the cause maybe.  But here are some ideas.  Did you try slowing the clock way down to see does the failing switch occur in a very simplified case? Another check to do is go around all the pins on the switch with a DMM and check the voltage levels and make sure they are what they should be.  We have seen issues with pcbs and floating pins in the past with some customer builds, e.g. ground pins not being ground.  A thought that comes to mind is its possible a higher frequency signal might get over some parasitic series capacitance problems better than a lower speed/DC signal which would be blocked.  Maybe there is something in that to give us a clue what's going on.  
      

      

      Eric.
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on May 19, 2022 4:02 PM
            
            
												
						in reply to EricC
					
									
        
	
        

		
		
        
					
        Hi Eric, 
        

        The voltages seem fine on all the pins. they are as expected. Another recent observation we had is that at lower frequency when we put a probe on The Y8 pin which is under use, the inconsistent switching goes away. Is there any impedance requirement for the output pins for the switch to work consistently? 
        

        Thanks
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on May 19, 2022 4:02 PM
            
            
												
						in reply to EricC
					
									
          
	
          

		
		
          
					
          Hi Eric, 
          

          The voltages seem fine on all the pins. they are as expected. Another recent observation we had is that at lower frequency when we put a probe on The Y8 pin which is under use, the inconsistent switching goes away. Is there any impedance requirement for the output pins for the switch to work consistently? 
          

          Thanks
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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