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LTC4267-3 Production
The LTC4267-3 combines an IEEE 802.3af compliant Powered Device (PD) interface with a 300kHz current mode switching regulator, providing a complete power...
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LTC4267-3 on Analog.com

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About problem of LTC4267-3

		
	
				

			

									
					    kshigemori281
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 29, 2021 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    Could you tell me about connection of PWRPD of LTC4267-3.
    Customer has made board nearly to non opto design of DC1249A.
    

    DC1249 and customer board is difference that Customer has used pull up 10kΩ resistance between PWRPG and PVcc and D8 is 7.5V zener diode. And Then they couldn't move board when it is low input voltage(45V).
    

    We predict that the resistance connected between PWRGD and PVcc may cause the PVcc voltage to drop, causing it to fall below the PVcc UVLO threshold and not operate.
    We have confirmed that it works when PWRGD is opened by actually following the data sheet.
    

    If the above recognition is correct, is the measure to open PWRGD correct?
    In addition, Last page of the data sheet is wrote 100KΩ , but is there any reason why 10K Ω is inconvenient?
    

    Best regards
    
			
    
			
									
		                             
                        

    
    
                                            
                 PoE Powered Device (PD)
                
                                                    
                 LTC4267-3
                
                                                    
                 Power-over-Ethernet (PoE) Interface Controllers
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Oct 6, 2021 7:55 PM
            
            
						
			            		
      
		
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      Hello,
      

      Your theory that the 10k resistor to PWRGD is pulling PVcc into UVLO sounds possible. But this 10k resistor should only draw less than a milliamp from PVcc, so it sounds like there could be something else going on here. Is there a reason why the customer does not want to change to 100k to match the reference design?
      

      

      Best Regards,
      

      Eric
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
				
				
				
		
		
      
			
		
      
	
      

      

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                on Oct 8, 2021 5:38 AM
            
            
												
						in reply to EHorsma
					
										
			            		
        
		
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        Thank you for the quick reply.
        

        Please let me know if you can find the other factor that makes the output come up only by removing the 10kΩ pull-up resistor between PWRGD and PVCC.
        

        Also, the customer can change 100kΩ, open, but would like to know what causes it not to work at 10kΩ.
        

        We would be grateful for your help.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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                on Oct 8, 2021 5:38 AM
            
            
												
						in reply to EHorsma
					
										
			            		
          
		
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          Thank you for the quick reply.
          

          Please let me know if you can find the other factor that makes the output come up only by removing the 10kΩ pull-up resistor between PWRGD and PVCC.
          

          Also, the customer can change 100kΩ, open, but would like to know what causes it not to work at 10kΩ.
          

          We would be grateful for your help.
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
				
				
				
		
		
          
			
		
          
	
          

          

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