Products Mentioned

LTC4267 Production
The LTC4267 combines an IEEE 802.3af compliant Powered Device (PD) interface with a current mode switching regulator, providing a complete power solution...
Datasheet
LTC4267 on Analog.com

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About the internal power MOSFET

		
	
				

			

									
					    Toku
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Feb 13, 2025 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  LTC4267 
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hello team,
    

    Under the conditions that the switching regulator of LTC4267 works normally(PWM enabled), 
    if an overcurrent flows on the secondary side(POE) and a current through the VPORTN 
    exceeds 350mA, will the current be limited to 350mA by controlling the FET shown below?
    

     
    

    Best regards, 
    
			
    
			
									
		                             
                        

    
    
                                            
                 PoE Powered Device (PD)
                
                                                    
                 Datasheet/Specs
                
                                                    
                 LTC4267
                
                                                    
                 Power-over-Ethernet (PoE) Interface Controllers
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Apr 10, 2025 5:39 PM
            
            
						
			            		
      
		
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      Hello,
      

      Sorry for the delayed response. Assuming we are considering current flowing in the conventional direction (POUT to VPORTN), then yes, the current will be limited to 375ma (typical). The PD interface includes dual level input current limit. At turnon, before the POUT load capacitor is charged, the PD current level is set to a low level. After the load capacitor is charged and the POUT – VPORTN voltage difference is below the power good threshold, the PD switches to high level current limit. The PD stays in high level current limit until the input voltage drops below the UVLO turn-off threshold.
      

      Best Regards,
      

      Eric
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
				
				
				
		
		
      
			
		
      
	
      

      

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                on Apr 10, 2025 9:07 PM
            
            
												
						in reply to EHorsma
					
										
			            		
        
		
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        Hello Eric,
        

        Thank you very much for your reply.
         I have inferred that the current was limited to 375mA from the Input Current Limit section on page 13 of the datasheet, but your response clarified that.
        

        Thank you and best regards,
        Tsuyoshi Tokumoto
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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