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LTC4353 OR-ing diode enabling below 0.8V not 0.6V



		

			

									
						plafountain
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on Mar 7, 2019 
				
			
			
		


				
		

		    		    
		    
		    	
			
Hello,


I am using the LTC4353 in the configuration shown in the attached image. My application requires that the AUX voltage be higher initially than the MAIN voltage so I would like to disable the AUX current path until the main voltage drops below 9V. I expect M2 to be disabled until the MAIN voltage drops below about 9V when the output of the divider should be roughly <0.6V. This is not happening currently, the AUX supply is enabled when the circuit is powered via 11.5V and 12.3V. Gate2 appears enabled below 0.8V. Not until I turn the main supply up to 12V or so is it disabled. I may be missing something very simple but it is essentially recreating the Typical Application circuit on page 11 of the datasheet, only modifying the input voltages and discretes to match.




 

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	














	

	

					



			


				
	









	
    
	

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                                 Analog Employees 
                                
                            
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                on Mar 16, 2019 1:02 AM
            
            
					
    
	
    

		
		
    
					
    Please note that there is a parallel current path through the inherent MOSFET body diode even if the MOSFET channel is turned off by driving its gate low. When MAIN = 11.5V and AUX = 12.3V, the output will be powered through M2 body diode to 12.3V – 0.7V = 11.6V (roughly). And M1 will be turned off since it sees -0.1V reverse voltage. The datasheet circuit works because those are 3.3V supplies and it’ll work if the difference between them is less than a diode voltage. For your application, please use the 2-channel prioritizer LTC4418: http://www.analog.com/LTC4418
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
						
				
				
		
		
    
			
		
    
	
    

    

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