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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 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user is experiencing an issue with the RUN pin of the LTC3855IUJ#PBF going high (~4V) despite being pulled low by an external power sequencer. The support engineer suggested checking the connection between the power sequencer and the LTC3855, as well as ensuring the power sequencer is not biased from INTVCC. The user confirmed there is no connection between the RUN pin and the power sequencer, and INTVCC is not connected to the sequencer.
                        	    
    
                
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    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.
    
			
    
			
									
		                             
                        

    
    
                                            
                 ltc3855
                
                                                    
                 Step-Down (Buck) Regulators
                
                                                    
                 Multiple Output Buck Regulators
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Dec 12, 2021 12:41 PM
            
            
						
			            		
      
		
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      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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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Dec 12, 2021 12:41 PM
            
            
						
			            		
      
		
										+1
					
	
      

		
		
      
		
      
                                
                                                            
      
					
      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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