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LT3478-1 Application Question



		

			

									
					    Circuit
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jan 23, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi all,
    

    

    Our company is looking to use the LT3478-1 device and we wanted to confirm if there is a known problem with the device becoming unstable at a given point as per these previous topics:
    

     RE: LT3478-1 Pulsates Under Some Circumstances 
    

     LED Driver 
    

    In both cases the pulsing was said to occur around 14-15Hz. We are simulating the system as per the recommended LTspice simulation and have not observed this. We only have made two small changes: 
    

    1. Removing the MOSFET since we don't need PWM dimming
    

    2. Increasing the input voltage to 25V and connecting our LED string which draws 0.2A at 40V. 
    
									
			        
		
    

				
						
        

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Feb 1, 2022 8:21 PM
            

            
					
      
	
      

		
		
      
					
      Hi Circuit,
      

      There is no know issues with LT3478-1. Instabilities typically stem from improper design of the power stage.
      

      Additionally, the absolute max rating of LED and OUT pins is 42V. A 40V string doesn’t leave much in terms of voltage headroom. If the spec of the LED string is 40V at cold and it will operate at lower voltage during room temp conditions, its probably okay to use. If 40V is the string voltage at room temp, I think another IC needs to be selected for use. You are going to have to put some tight restrictions on the output regulation voltage (OVP) to ensure that if the LED string is removed, the output voltage does not climb beyond 42V.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Feb 1, 2022 8:21 PM
            

            
					
      
	
      

		
		
      
					
      Hi Circuit,
      

      There is no know issues with LT3478-1. Instabilities typically stem from improper design of the power stage.
      

      Additionally, the absolute max rating of LED and OUT pins is 42V. A 40V string doesn’t leave much in terms of voltage headroom. If the spec of the LED string is 40V at cold and it will operate at lower voltage during room temp conditions, its probably okay to use. If 40V is the string voltage at room temp, I think another IC needs to be selected for use. You are going to have to put some tight restrictions on the output regulation voltage (OVP) to ensure that if the LED string is removed, the output voltage does not climb beyond 42V.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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