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AD4111 open wire detection



		

			

									
						Cerberus
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jan 18, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    We are going to use AD4111 in our project.
    

    We want 4 single-ended bipolar ±10 V voltage inputs, the input pins are VIN0~VIN3.
    

    Open wire detection function is necessary.
    

    Here are my questions：
    

    

    1. In datasheet, It says “The VIN0 and VINCOM pins are left floating. Nothing is connected to the pins.” in example 1. 
    

    But I think VINCOM needs connected to GND, is that right?
    

     
    

    

    2. When I configure the registers of VIN1，I should configure CHANNEL REGISTER 1 （CH1）and CHANNEL REGISTER 2（CH2）INPUT bits to 0000110000. 
    

    Make sure the input pair（VIN1, VINCOM）is connected to channel 1 and channel 2. Is that right?
    

     
    

    

    3. When I select the input pair（VIN0, VINCOM）connected to the channel 0 and channel 15. I wonder how the chip is connected inside. Why they have two different output code? 
    

    Do the channel 0 connect like this？
    

     
    

    And the channel 15 connect like this？
    

     
    

    

    4.I also want to know the specific principle and process of open wire detection. What is COMPA pin used for？
    

     
    

    Thank you very much！
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

					
    
			
    


    

	















    
	
    
	
    
					



			


				
	









	
      
	

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													+1
							
			
				
									
							        
			
			
			
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                on Jan 19, 2022 3:29 AM
            
            
					
      
	
      

		
		
      
					
      Hi, 
      

      1. Yes, in single ended mode the VINCOM is connected to GND. 
      

      2.  Yes, channels must be assigned to specific channel pair. So if you want to use VIN1 and VINCOM then the channel pair required is CH1 and CH2.
      

      For your question 2 and 3. We do not disclose in public the internal operation of the OWD feature as it is Protected by U.S. Patent 10,852,360. But we provided in the datasheet how to detect an open wire using this built-in feature.
      

      So In general, in order to detect an Open wire fault the difference between the two channel conversions must be compared to a certain threshold level. And this threshold is equivalent to 300mV. If the difference of these two channel conversions is greater than the threshold voltage, an open wire fault has occurred. If the difference is less than the voltage threshold, then there is no open wire fault. And this must be support in the user software. The threshold had been determined during the evaluation/characterization of this part with the requirement of additional capacitor (680 pF) and resistor (1 kΩ) applied and connected in series between each compensation pin (COMPA, COMPB) and voltage input pin.
      

      Another thing to take note here is since two channel conversion is required, This effectively halves your throughput rate.
      

      Thanks,
      

      Jellenie
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
        
            
			                            
                        
                on Jan 19, 2022 5:16 AM
            
            
												
						in reply to JellenieR
					
									
        
	
        

		
		
        
					
        Thank you for answering my question.
        Your answer is very clear and easy to understand.
        Sorry for asking the patent-related questions.
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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