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LT8650S Recommended for New Designs
The LT8650S is a dual step-down regulator that delivers up to 4A of continuous current from both channels and supports loads up to 6A from each channel...
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LT8650S on Analog.com

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Adding 68µH inductor before EMI filter at input

		
	
				

			

									
					    mehdiaghayi
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Dec 7, 2025 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user asked if adding a 68μH inductor (SRN4018BTA-680M) before the EMI filter on the LT8650S demo board (DC2407A) is recommended to reduce conducted emissions. The final answer suggests using a CLC pi filter for EMI suppression and recommends designing the filter with LTPowerCAD to visualize conducted EMI. Experiments by the user found that adding a large inductor at the input made the LT8650S unstable and had no effect on EMC improvement.
                        	    
    
                
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    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  LT8650S  
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hello,
    

    In order to reduce conducted emission is it recommended to place a 68µH inductor (SRN4018BTA-680M) before EMI filter mentioned in (DC2407A) at the input voltage? 
    

    the switching frequency of LT8650S is 2Mhz and by which a CAN interface will be powered.
    

    Thank you!
    
			
    
			
									
		                             
                        

    
    
                                            
                 Datasheet/Specs
                
                                                    
                 emc
                
                                                    
                 Internal Power Switch Buck Regulators
                
                                                    
                 LT8650S
                
                                                    
                 Step-Down (Buck) Regulators
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Dec 8, 2025 10:33 AM
            
            
						
			            		
      
		
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      Hi,
       
      We recommend a CLC pi filter on the input for EMI suppression, like that shown in the demo board. You do not necessarily need to add another inductor before the pi filter. 
       
      Additionally, if you design your converter using LTPowerCAD, there is a tool in the tool bar on the first page that allows you to design your input pi filter and visualize the conducted EMI for different standards. It looks like this when you load the design tool for the LT8650S:
       
       
      Thanks!
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
				
				
				
		
		
      
			
		
      
	
      

      

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                on Dec 11, 2025 9:24 AM
            
            
						
			            		
        
		
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        Hi,
        


        after some experiments I've found that adding a big inductor at the input of LT8650S make it unstable and also has not effect on EMC improvement.
        

        Using LTpowercAD for analysing the power supplie regarding the EMC was a very good suggestion,
        

        

        thank you so much for your answer.!
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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