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The LTC2944 measures battery charge state, battery voltage, battery current and its own temperature in portable product applications. The wide input voltage...
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LTC2944 on Analog.com

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What is "the offset of the internal op amp"

		
	
				

			

									
					    mtwieghr
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Aug 24, 2025 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  LTC2944 
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hi all.
    

    The LTC2944 datasheet says the following:
    

    

    For input signals with an absolute value smaller than the
    offset of the internal op amp the LTC2944 stops integrating
    and does not integrate its own offset
    

    

    Is this equivalent to Vose in the electrical characteristics (5uV typ/10uV max)? I don't see any other offset specification relating to the coulomb counter.
    

    Regards,
    

    Mike
    
			
    
			
									
		                                 
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                 ltc2944
                
                                                    
                 Datasheet/Specs
                
                                                    
                 Battery Fuel Gauge and Coulomb Counter
                
                                                    
                 battery management
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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                on Aug 31, 2025 1:51 PM
            
            
						
			            		
        
		
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        Any help here?
        

        I tried to test it by drawing a small constant current and observing how fast ACR changes over the course of ~10 minutes. My Rsense value is 1mohm.Prescaler was 256, so each LSB of the ACR is 1.0625mAhr.
        

        


        
Actual current (mA)
ACR rate of change (LSB/hr)
Measured current (mA)

        

        
20.0
0
0.0

        

        
40.0
9.1
9.7

        

        
60.0
37.6
39.9

        

        
80.0
61.3
65.2

        
        

        

        So there is apparently a level of current that the LTC2944 cannot detect. At 20mA, the ACR had not changed even after a full hour. Based on the datasheet Vose I would expect it to respond to currents above 10mA, but apparently that's not the case.
        

        And even when the current is high enough for the ACR to change, it has far greater error than I would expect compared to the datasheet Vose value. But I see that the Vose spec is for the condition Vsense > 500uV, and the plot for "Total Charge Error vs Differential Sense Voltage" also only extends down to Vsense=500uV. Could it be that Vose is actually much greater at lower sense voltages?
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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