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The AD7908 / AD7918 / AD7928 are, respectively, 8-bit, 10-bit, and 12-bit, high speed, low power, 8-channel, successive approximation ADCs. The parts operate...
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AD7928 on Analog.com

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AD7928: Extend external reference voltage range to 5V.

		
	
				

			

									
					    KaHu
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 4, 2025 
				
			
			
		
    
		
		                    	    
    
        	    
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                The user inquired about the impact on accuracy of the AD7928 when using a 5V reference voltage instead of the specified 2.5V. The final answer confirmed that while the relative accuracy in LSB terms remains the same, the absolute error in volts doubles due to the increased LSB size. The accompanying answer clarified that measuring a 5V signal with either a 2.5V reference and extended range or a 5V reference yields the same absolute error.
                        	    
    
                
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    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  AD7928  
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hi, I'm wondering about effect on accuracy on AD7928 when using 5V instead of 2,5V external reference voltage.  Datasheet request is 2.5V +/-1% specified perfomance. REFin to AGND can be set to AVdd. Would it double offset and gain error only or are there other effects to consider like nonlinearity? Thanks
    
			
    
			
									
		                             
                        

    
    
                                            
                 Datasheet/Specs
                
                                                    
                 ad7928
                
                                                    
                 Multiplexed A/D Converters
                
                                                    
                 Precision A/D Converters
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Nov 6, 2025 3:54 AM
            
            
						
			            		
      
		
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      Hi,  .
      

      

      Your interpretation is correct. Let’s perceive this in terms of LSB size for clarity. With a 2.5 V reference, each LSB corresponds to approximately 0.61 mV. If we increase the reference to 5 V, the LSB doubles to about 1.22 mV. Since most error specifications such as offset, gain, and INL, are expressed in LSBs, their absolute voltage impact also doubles when the LSB size doubles. In other words, the relative accuracy in LSB terms remains the same, but the absolute error in volts scales proportionally with the reference voltage.
      

      

      Regards,
      Jo
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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                on Nov 6, 2025 10:05 AM
            
            
												
						in reply to NathanT
					
										
			            		
        
		
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        Hi Jo,
        

        thank you for clarification. In other words measuring a 5V signal with 2,5V reference voltage and extended range or 5V signal with 5V reference provides the same result and absolute error. Best Regards
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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