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LT8391 Recommended for New Designs
The LT8391 is a synchronous 4-switch buck-boost LED controller that regulates LED current from input voltage above, below, or equal to the output voltage...
Datasheet
LT8391 on Analog.com

LT8391A Recommended for New Designs
The LT8391A is a synchronous 4-switch buck-boost LED controller that regulates LED current from input voltage above, below, or equal to the output voltage...
Datasheet
LT8391A on Analog.com

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LT8391 Flashing



		

			

									
					    SunStone
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 30, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi All, 
    

    As power is increased to about 42 watts (42V @ 1amp) LED output starts flashing.  Noticed SS pin is dropping low quickly.  From the data sheet page 13 I see 5 conditions that would cause a rapid discharge of the SS pin.  They are CTRL 1 or 2 below 0.2V, UVLO low, Visp-Visn > 0.75V,  and FB > 1.05V.  I dont see any of these conditions being broken.  The SS cap is being quickly discharge do switch to ground from Inhibit Control looks like its being activated.  What could be going on?
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
			                            
                        
                on Apr 22, 2021 9:40 AM
            
            
					
      
	
      

		
		
      
					
      Hi SunStone,
      

      If you say flashing, do you mean that the LED outputs are blinking on and off? The LT8391 has a fault protection and detection feature that provides information whether there is an open or short LED. The complete cycle of fault detection and shutdown can be seen on page 17 of the data sheet. After the start-up sequence has been initialized, the circuit will try to run and detect if there is fault (open or short LED). the dropping of SS pin is a result of this fault protection where it is pulled low in and then the switch is disabled after the soft-start is pulled low. The IC will try to check if there is still fault and will repeat again until the fault is corrected. Since the switch is enabled and disabled in cycles, this may be the result why the LED outputs are blinking (turning on and off).
      

      For a more detailed information and discussion about the fault protection and its cycle, check page 17 of the data sheet.
      

      Regards
      

      Siglo
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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