Products Mentioned

LT3507A Production
The LT3507A is a triple, current mode, DC/DC converter with internal power switches and a low dropout regulator. The switching converters are step-down...
Datasheet
LT3507A on Analog.com

Thread Details

  • State Verified Answer
  • Replies 1 reply
  • Subscribers 39 subscribers
  • Views 106 views
  • Users 0 members are here
Related Content

        

            Post
             Go back to editing
        

    

    


    

    









		


















	
	
			
	
			
		
	
	
		

	    
	    
	    		
Input Voltage Drop from 32 Volt to 15 Volt

		
	
				

			

									
					    thodie
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Feb 16, 2026 
				
			
			
		

		
		                     
				
        		

		    
		    		    

		      		            		        
Category: Hardware

    		        		            		    
Product Number:  LT3507A  

    		        		    		    

		    		    
		    			

			    
Hello,
 
 we are using the LT3507A to generate with the Input voltage (10 - 32 Volt) the three output Voltages 5 Volt, 3,3 Volt and 1,35 Volt. 


We have an voltage drop of the input voltage supply from 32 volts to 15 volts (see yellow signal in screenshot). Then all of the three output voltages drops, too. In the Screenshot the purple signal represents the 5 Volt. The 5 Volts decreased to 2.4 Volts. 


The switch node (light blue signal in screenshot) stop to work for a little while. Then the LT3507A starts again to work and the voltages increase again.
 The processor, which are powered by these three voltages, stop working proper.
 Is there a way to figure out why the LT3507A behaves like this?




  

			

			
									
		                             
                        

    

                                            
                 hardware
                
                                                    
                 switching regulators
                
                                                    
                 LT3507A
                
                                                    
                 Step-Down (Buck) Regulators
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			


				
	









	
    
	

  • 
	
    



	
			
		
	



    
	
    
		
    
							
					
    
		
    
		    
		    		    
			
				
									
							        
			
			
			
    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Feb 19, 2026 4:35 AM
            
            
						
			            		
    
		
										0
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    Hello,
    If the your design can work at 15V continuously during steady state, the sudden stop may link to some controller requirement not meet during transient or drop of the input. I tried to check this with LTspice and unable to replicate. It might be something with the selected components. What I can suggest is, try to design your circuit with LTspice and compare the behavior in your actual board. 
     
    Possible root causes: 
    Internal bias UVLO triggered during the VIN transient
    Peak current limit + control loop saturation, forcing a restart
    BIAS pin droop due to how it is sourced
    Frequency foldback + soft‑start delay, making recovery visible
     
    For debugging try to check the list:
    Scope VIN, BIAS, SW, and VC during the transient
    Check if BIAS < UVLO threshold even briefly
    Add bulk capacitance at VIN close to the IC
    Power BIAS from a stable external rail if available
    Verify UVLO divider isn’t set too aggressively
    Check peak inductor current vs current limit at low VIN
     
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
				
				
				
		
		
    
			
		
    
	
    

    

    •