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LT3845A Recommended for New Designs
The LT3845A is a high voltage, synchronous, current mode controller used for medium to high power, high efficiency supplies. It offers a wide 4V to 60V...
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LT3845A on Analog.com

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Duty-cycle up to 100%

		
	
				

			

									
					    SteScre
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Dec 9, 2025 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user inquired about using the LT3845A at 100% duty cycle for 300ms to maintain an output voltage equal to the input (24V-32V) before dropping to 15V. The final answer indicated that the LT3845A cannot operate at 100% duty cycle, but suggested the LTC3824 and LTC3864 as alternatives that can. For space applications, the LT8650S can operate up to 99% duty cycle in burst mode, or a prioritizer can manage two voltage sources.
                        	    
    
                
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    Category: Hardware
    
    		        		            		    
    Product Number:  LT3845A  
    
    		        		    		    
    
		    		    
		    			
    
			    
    Dear All,
    

    I've a question about maximum duty-cycle of LT3845A.
    

    In our application, starting from a 28V bus (range 24V - 32V), we need an output voltage which is equal to input bus for a definite time (< 300ms) and than goes down to 15V.
    

    Is it possible to use this PWM controller, running it at 100% duty cycle for the first 300ms?
    

    Thanks in advance for your reply.
    

    Kind Regards
    

    Stefano
    
			
    
			
									
		                             
                        

    
    
                                            
                 LT3845A
                
                                                    
                 hardware
                
                                                    
                 External Power Switch Buck Controllers
                
                                                    
                 Step-Down (Buck) Regulators
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Dec 9, 2025 10:31 AM
            
            
						
			            		
      
		
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      Hi,
       
      Unfortunately, the LT3845A does not operate at 100% duty cycle. We do make a couple of similar buck converters that can operate at 100% duty cycle. A couple of examples would be the LTC3824 and the LTC3864. Alternatively, you could look at using a buck-boost converter instead.
       
      Thanks!
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
				
				
				
		
		
      
			
		
      
	
      

      

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                on Dec 9, 2025 10:45 AM
            
            
						
			            		
        
		
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        Hi,
        

        thank you very much for your gently reply.
        

        We're looking for a solution that could perhaps also be used in space applications in the future.
        

        Do you have any PWM controllers you'd recommend?
        

        Thanks in advance
        

        Stefano
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        
            
						
                            
            
            				
            
                on Dec 9, 2025 11:06 AM
            
            
						
			            		
        
		
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        Hi,
         
        For space applications, we currently do not have any converters other than buck converters. That being said, the LT8650S will work in burst mode up to 99% duty cycle. 
         
        If that is still not good enough, you may need to have two voltage sources (the input and the converter output) both connected to your load through some sort of prioritizer, that way you can apply the two separate voltages at different times.
         
        Thanks!
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
						
				
				
				
		
		
        
			
		
        
	
        

        

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                on Dec 9, 2025 11:15 AM
            
            
						
			            		
          
		
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          Hi,
          

          We are actually studying a solution with two sources and a mosfet system that directs the two voltages, but since this system would have to be applied on 9 distinct lines, the number of mosfets needed is becoming considerable.
          

          Thank you very much for your support.
          

          

          Regards
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
				
				
				
		
		
          
			
		
          
	
          

          

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