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LTC4121EUD charge when Vin<12V



		

			

									
						artur@nelsystems.ru
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jun 26, 2018 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Only at an input voltage >12V PWM occurs and the charging current appears (0.14A input current). Otherwise, there are no signals. The charge status and error are read at <12 volts as well as at >12 volts at the input: nCHG = 0, nFLT = 1.
    
 
    I need Vfloat = 4.0-4.2V, batery voltage which I try to charge V=3.5V. Vin=6-8.4V (two LiPo cells), Vout=4V (single cell LiFePO4).
    
 
    May be only LTC4121-4.2 can work with <12Vin? But I need Adj Vfloat.
    
 
    What should I do to start PWM on low voltage with LTC4121EUD?
    
 
    PS. When Vin < 12V Vfloat avg = 2.74V, voltage ripple with a frequency of 1/280 ms, Vp-p=2.7-2.8V looks like a saw.
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

					
    
			
    


    

	















    
	
    
	
    
					



			








	
	
	
	



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                on Jul 18, 2019 8:39 AM
            
            
					
        
	
        

		
		
        
					
        Good morning, we also have had similar issue. 
        

        LTC4121 do not charge battery if input voltage was greater than 10V, our inductor is 68uH and charging current is 220mA for a single LiFePo4 battery. 
        

        We have solved by inserting a 10 ohm resistor in series with boost capacitor and changed this from 22nF to 100nF. Our layout is 2 layers PCB with standard thickness 1.6mm. 
        

        Of course this IC remains strongly sensitive to layout and shows some silicon issues.
        

        Regards, Luca 
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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													0
							
			
				
									
							        
			
			
			
          
            
			                            
                        
                on Jul 18, 2019 8:39 AM
            
            
					
          
	
          

		
		
          
					
          Good morning, we also have had similar issue. 
          

          LTC4121 do not charge battery if input voltage was greater than 10V, our inductor is 68uH and charging current is 220mA for a single LiFePo4 battery. 
          

          We have solved by inserting a 10 ohm resistor in series with boost capacitor and changed this from 22nF to 100nF. Our layout is 2 layers PCB with standard thickness 1.6mm. 
          

          Of course this IC remains strongly sensitive to layout and shows some silicon issues.
          

          Regards, Luca 
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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