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The ADuM3210/ADuM3211 are dual-channel, digital isolators based on Analog Devices, Inc., iCoupler® technology. Combining high speed CMOS and monolithic...
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ADUM3211 on Analog.com

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The refresh pulses of ADuM3211



		

			

									
					    AndrewLu
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Apr 24, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi, the ADuM3211 is employed in the isolation COMM of CAN and RS485.  Now it seems the isolator caused negative EMI issue with the GPS module nearby, when MCU is active but the COM line is unplugged. In datasheet(page 17) it mentions a periodic set of refresh pulses to ensure dc correctness, so I have questions about this mechanism.
    

    1.What's the frequency and the duty cycle of the refresh pulses? 
    

    2.What's the meaning of the so-called "Unpower" in Table 35? Is it a real low-power state, or an assumption of the non-functoinality?
    

    3.Can I disable the refresh pulses by disabling the COM port of MCU and unplugging the COM line at the same time?
    

    Many thanks!
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 Digital Isolation Technology
                
                                                    
                 ADuM3211
                
                                                    
                 Standard Digital Isolators
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
			                            
                                                                                                                        
            
				
			
            
					
      
	
      

		
		
      
					
      Hi Andrew, 
      

      The ADuM3211 is an edge encoding architecture. The isolator sends either a single or double pulse when the input detects a state transition. If the input does not detect a change within ~1us, it will send a refresh pulse. The refresh is for DC correctness, in case the output was somehow upset. The refresh pulses will be sent continuously with a DC input state, and they cannot be disabled.  
      

      If you have access to a scope, a probe can be placed between the bypass cap and the VDDx pin. If you set the scope with a DC offset, and look at the signal in one of the smaller mV ranges, you should be able to see the current pulses when the transmitter is active. 
      

      "Unpowered" means the supply is below the valid supply range. I recommend bring the supply to less than 0.5V to consider the device unpowered.  
      

      There are newer On-Off Keying architecture isolators available with the same pin-out. See the ADuM121N for the ADuM3211. These devices encode the state at the input, and do not have a refresh pulse. When isolator transmits in the non-default state, and effectively does nothing in the default state.  
      

      The ADuM3211 is a default low isolator. This means when the input side is unpowered, the output channel will go low. CAN transceivers transmit a dominant state when TXD is low. I would advice switching to a default high (ADuM3201 or ADuM121N1) to avoid CAN bus interruptions in case the logic side becomes unpowered. 
      

      Regards,
      

      Jason
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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