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The AD4003 / AD4007 / AD4011 are high accuracy, high speed, low power, 18-bit, Easy Drive, precision successive approximation register (SAR) analog...
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AD4003 on Analog.com

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AD4003 negative output

		
	
				

			

									
					    Rohit_Cap
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 10, 2022 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user is experiencing sign reversal in the ADC output when using the AD4003 in 3-wire turbo mode with a 100 MHz clock and a 3V differential input signal. The issue is due to the common mode input voltage being out of spec (1.5V instead of 2.5V for a 5V VREF). The solution involves using a fully differential amplifier like the ADA4940 or ADA4945 to meet the common mode input voltage requirement, or switching to the single-ended AD4002.
                        	    
    
                
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    Hi,
    

    I am using AD4003 ADC in one of the design. In this we are using 3-wire turbo mode.
    

    Clock frequency used is 100Mhz.
    

    Now when I provide 3V differential signal to the input of ADC. I am getting a hex value 0x2D0CD which is near to -3V(Read on SDO line).
    

    My question is why I am getting output of ADC with sign reversal?
    

    

    Regards,
    

    Rohit
    
			
    
			
									
		                             
                        

    
    
                                            
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Mar 11, 2022 9:40 AM
            
            
												
						in reply to Rohit_Cap
					
										
			            		
      
		
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      Thanks Rohit.
      

      You are using VREF = 5V, correct?
      

      If so, then the Common Mode Input Range specification is being violated and would explain why the output code is invalid.
      

      The common mode input range spec refers to the average voltage between IN+ and IN- pins. Nominally the common mode input voltage should be VREF/2. For 5V VREF this would bee 2.5V.
      

      For the 3V and 0V configuration above, the common mode input voltage is 1.5V, which is out of the min/max spec range in the data sheet.
      

      Achieving this common mode input voltage requirement can be done with devices such as fully differential amplifiers (see ADA4940, ADA4945, etc.)
      

      Alternatively, the AD4002 is a single-ended version of the AD4003, where the IN- input can be tied to ground and there are no common mode input voltage requirements (since it's not a differential device).
      

      Thanks,
      

      Tyler
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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                on Mar 11, 2022 9:55 AM
            
            
												
						in reply to tschmitt
					
										
			            		
        
		
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        ok thanks I will check and solve this issue.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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