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LT3763 Production
The LT3763 is a fixed frequency, synchronous, step-down DC/DC controller designed to accurately regulate output currents up to 20A. The average current...
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LT3763 on Analog.com

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LT3763 gets very hot and breaks



		

			

									
					    MathWest
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 25, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi. I have problems with LT3763.
    

    As a DCDC-converter with current limitation, this IC should load large capacities (10mF) up to max.12V.
    After switching on the power supply, the IC gets very hot and breaks. Short circuit between Pin26 (SW) and GND. 
    This also happens without a load at the output. 
    Supply voltage:  48VDC, Output voltage: 12V, Max output current: 2.77A.
    

    The IC is switched on via an MCU
    


    I'v checked all but I have no idea what is wrong.
    

    LT3763_Gerber.zip  
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                        
                on Mar 30, 2022 5:19 AM
            
            
					
      
	
      

		
		
      
					
      Hi MathWest,
      

      Can you double check your chosen MOSFETs? Make sure they are properly rated. Please follow the layout guidelines found on page 22 or copy the demo board layout as close as possible.
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Apr 4, 2022 3:36 PM
            
            
												
						in reply to ron.p
					
									
        
	
        

		
		
        
					
        Hi ron.p
        

        New MOSFETs are OK.
        The circuit behaves as desired.
        

        In my calculation I strictly adhered to the data sheet. That was wrong.
        In which cases do you have to follow the redommendation in the data sheet?
        

        Page 14, Data sheet "Switching MOSFET selection"
        

        "A good approach to MOSFET sizing is to select a high side
        MOSFET        , then select the low side MOSFET. The trade-
        off between R        DS(ON), QG, QGD and QGS for the high side
        MOSFET is shown in the following example        . V O is equal
        to         4V. Comparing two N-channel MOSFETs, with a rated
        V        DS of 40V and in the same package, but with 8× different
        R        DS(ON) and 4.5× different QG and QGD:
        M        1: RDS(ON) = 2.3mΩ, QG = 45.5nC,
        Q        GS = 13.8nC, QGD = 14.4nC, RG = 1Ω
        M        2: RDS(ON) = 18mΩ, QG = 10nC,
        Q        GS = 4.5nC, QGD = 3.1nC, RG = 3.5Ω"
        

        I think the same MOSFETs with low Qg are a better choice.
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Apr 4, 2022 3:36 PM
            
            
												
						in reply to ron.p
					
									
          
	
          

		
		
          
					
          Hi ron.p
          

          New MOSFETs are OK.
          The circuit behaves as desired.
          

          In my calculation I strictly adhered to the data sheet. That was wrong.
          In which cases do you have to follow the redommendation in the data sheet?
          

          Page 14, Data sheet "Switching MOSFET selection"
          

          "A good approach to MOSFET sizing is to select a high side
          MOSFET          , then select the low side MOSFET. The trade-
          off between R          DS(ON), QG, QGD and QGS for the high side
          MOSFET is shown in the following example          . V O is equal
          to           4V. Comparing two N-channel MOSFETs, with a rated
          V          DS of 40V and in the same package, but with 8× different
          R          DS(ON) and 4.5× different QG and QGD:
          M          1: RDS(ON) = 2.3mΩ, QG = 45.5nC,
          Q          GS = 13.8nC, QGD = 14.4nC, RG = 1Ω
          M          2: RDS(ON) = 18mΩ, QG = 10nC,
          Q          GS = 4.5nC, QGD = 3.1nC, RG = 3.5Ω"
          

          I think the same MOSFETs with low Qg are a better choice.
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

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