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LTC3855 Production
The LTC3855 is a dual PolyPhase® current mode synchronous step-down switching regulator controller that drives all N-channel power MOSFET stages. It includes...
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LTC3855 on Analog.com

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LTC3855 Enable control issue



		

			

									
					    rmalavi
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Dec 7, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi,
    

    I am using LTC3855IUJ#PBF as 10V to 6V buck regulator. we are using both the channels for same voltage generation.
    

    Observed that when I applied 10V to VIN pin, RUN pin of regulator goes high ~4V even though pulled low from external power sequencer.
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                        
                on Dec 12, 2021 6:41 PM
            
            
					
      
	
      

		
		
      
					
      Hello,
      

      The RUN pin of the LTC3855 should stay low when the sequencer pulls it low. The RUN pin of the LTC3855 is an input only with a 1uA pullup when the RUN pin is low and a 5.5uA combined pullup when the RUN pin is high. Check the connection between the power sequencer and the LTC3855. Also check the power sequencer itself. In addition, make sure the power sequencer is not biased from INTVCC since INTVCC will only turn on until the RUN pins are high (see page 12 of the D/S, Shutdown and Start-Up section, 1st paragraph).
      

      Best regards,
      

      Mike
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Dec 14, 2021 10:16 AM
            
            
												
						in reply to mike.shriver
					
									
        
	
        

		
		
        
					
        Hi Mike,
        

        There is no connection between RUN pin of LT3855 & power sequencer as I isolated by removing series 0ohm resistor.
        

        also INTVCC is not connected to power sequencer by any way.
        

        

        Thanks
        

        Rupesh
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        
            
			                            
                        
                on Dec 14, 2021 7:11 PM
            
            
												
						in reply to rmalavi
					
									
        
	
        

		
		
        
					
        Hello Rupesh,
        

        It looks like you have found the problem. Let me know if you need any more help.
        

        Best regards,
        

        Mike
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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