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LTC2688 high reference voltage

		
	
				

			

									
					    JKaufmann
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Aug 21, 2025 
				
			
			
		

		
		                    	    

        	    
Thread Summary

                The user asked about the effects of setting the reference voltage higher than Vcc - 0.6V or Vcc above 5.25V on the LTC2688. The final answer revealed that the issue was due to an error in the datasheet regarding the external reference overrange span. Operating outside the recommended range can cause internal buffer saturation, loss of linearity, and accuracy, but the user found the risk acceptable when setting the span to non overrange.
                        	    

                
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Category: Datasheet/Specs

    		        		            		    
Product Number:  LTC2688  

    		        		    		    

		    		    
		    			

			    
The datasheet specifies, that the reference voltage should be 0.6V lower than Vcc and Vcc should be at most 5.25V. What would be expected to happen if the reference voltage is larger than Vcc-0.6V, but still smaller than Vcc? Alternatively what would be expected to happen if Vcc is larger than 5.25V? In any case the voltages obviously stay within the absolute maximum ratings.

			

			
									
		                             
                        

    

                                            
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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Aug 24, 2025 11:04 PM
            
            
						
			            		
    
		
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    Hi,
    

    Operating the LTC2688 with a ref voltage greater than Vcc - 0.6V or a supply voltage exceeding 5.25V is not recommended. Violating the reference headroom can cause the internal buffer to saturate, leading to possible loss of linearity and accuracy. Exceeding the recommended supply voltage might result as well to the performance guarantees indicated in the DS not hold true and can possibly subject the device to thermal and electrical stress. For predictable and reliable performance, it is essential to operate the LTC2688 strictly within the recommended operating conditions as specified in the DS.
    

    Regards,
    

    Den
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
						
				
				
		
		
    
			
		
    
	
    

    

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                on Aug 25, 2025 2:38 AM
            
            
												
						in reply to dendalisay
					
										
			            		
    
		
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    Nothing unreasonable then.

    I later found out that the problem i had was due to an error in the datasheet. In Table 15, it states that for external references, the overrange span is the same as the non overrange span, which is not the case. This caused some confusion. When setting the span to non overrange the output matches what we expected.

    I know that using values outside the recommended opperating range can lead to problems, but in this case the risk is acceptable.
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
						
						
				
				
		
		
    
			
		
    
	
    

    

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