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LTC3630 Recommended for New Designs
The LTC3630 is a high efficiency step-down DC/DC converter with internal high side and synchronous power switches that draws only 12μA typical DC supply...
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LTC3630 on Analog.com

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LTC3630 never reaches 15V

		
	
				

			

									
					    HoC
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on May 17, 2023 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user is experiencing an issue with the LTC3630 regulator where the output voltage is 10.2VDC instead of the expected 15VDC. The final answer clarifies that both VPRG pins should be grounded to set the output voltage externally using a resistor divider. The user confirms they are using the correct configuration as shown in the datasheet, but the issue persists in real life despite working in LTSpice simulations.
                        	    
    
                
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    Category: Hardware
    
    		        		            		    
    Product Number:  LTC3630 
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hi,
    

    I have an issue with the LTC3630.  I am supplying the regulator with 30VDC and the output should be +15VDC. VPRG1 is connected to  SS and VPRG2 to GND, therefore VFB is set to 5V. With the external  divider R1 = 200k and R2 = 100k the output should be 15V. But unfortunately the output is always about 10.2VDC.  Current draw is around 30mA.
    

    

    Here the schematic:
    

     
    

    

    Any clues, why the 15V are never achieved. 
    

    Thanks in advance!
    

    Christian
    
			
    
			
									
		                             
                        

    
    
                                            
                 hardware
                
                                                    
                 Internal Power Switch Buck Regulators
                
                                                    
                 Step-Down (Buck) Regulators
                
                                                    
                 LTC3630
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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							FormerMember
					
      
		
      
		    
		    		    
			
				
									FormerMember
							        
			
			
			
    
            
						
                            
            
            				
            
                on May 22, 2023 7:45 PM
            
            
						
			            		
    
		
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    Hello,
    

    See snipped pin description below.
    

     
    

    

    If you want to set the output voltage externally by divider resistor, BOTH VPRG ARE SUPPOSED TO BE GROUNDED.
    

    What you did was set it to an output voltage of 5V. IT SETS OUTPUT VOLTAGE, NOT VFB VOLTAGE.
    

    

    Regards,
    

    Jhun
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    


	

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                on May 23, 2023 10:51 AM
            
            
												
						in reply to FormerMember
					
										
			            		
      
		
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      Hi Jhun,
      

      

      Thank you for your reply.
      

      I am aware of the output selection. If you go to the next chapter you see this configuration, which I am using in my application
      

      

       
      

      

      I also ran some simulations in LTSpice, which works perfectly there. But unfortunately in real life it is not working!!!!
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
				
				
				
		
		
      
			
		
      
	
      

      

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                on Jul 15, 2025 3:46 PM
            
            
												
						in reply to HoC
					
										
			            		
        
		
										+1
					
	
        

		
		
        
		
        
                                
                                                            
        
					
        Was this issue resolved? I will  use it this setup in one of my designs
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
						
				
				
				
		
		
        
			
		
        
	
        

        

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                on Jul 15, 2025 8:10 PM
            
            
												
						in reply to GuilleD
					
										
			            		
          
		
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          Hi  ,
          

          It seems like that the original poster had got the Vprg1 and Vprg2 pins swapped in his/her symbol, thus the internal feedback was set to 3.3V and therefore the output voltage was 10.2V. Make sure that Vprg1 (pin 7) goes to SS and Vprg2 (pin 6) goes to GND and use 2:1 external resistor divider for 15V (or 3.54:1 if Vprg1=GND and Vprg2=SS).
          

          So I'd say it is safe to use that chip and setup.
          

          Cheers, heke
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
				
				
				
		
		
          
			
		
          
	
          

          

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