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LT1166 Current Limit Function



		

			

									
					    Kazu
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Feb 18, 2018 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi All,
    
 
    Here is a question about the current limit if the LT1166. My circuit is almost the same as Figure 9. in the datasheet
    
 
    and I have attached it. I'd like the current limit to work more than 1A so I selected the 1.3 ohm Rsense.
    
 
    However the output current clamped about 3.6A peak as attached LTSpice simulation result [V(n012)=Vin, V(n009)=Vout, I(R9)=Iout].  Why is not the output current clamped about 1A? Is my understanding about the current limit function wrong?
    
 
    Regards,
    
 
    Kazu
    
								
    

				
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      •  Analog Employees  
      
            
			                            
                        
                on Mar 1, 2018 10:42 PM
            
            
					
      
	
      

		
		
      
					
      The current limit function is not a smooth function, but rather a hysteretic trip point (and not very precise) that shuts down the output stage for a period of time set by capacitances in the circuit (was only intended to minimize FET stress in a fault condition). If you have a specific current limit in mind, it isn’t too hard to add a transistor to each FET that will form a fast limiter function (the sense resistor could turn on a Vbe and the transistor collector could shunt away gate current from the FET).
      
 
      If fairly accurate and/or variable current control is of interest, one might consider an LT1970-based circuit.
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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      •  Analog Employees  
      
            
			                            
                        
                on Mar 1, 2018 10:42 PM
            
            
					
      
	
      

		
		
      
					
      The current limit function is not a smooth function, but rather a hysteretic trip point (and not very precise) that shuts down the output stage for a period of time set by capacitances in the circuit (was only intended to minimize FET stress in a fault condition). If you have a specific current limit in mind, it isn’t too hard to add a transistor to each FET that will form a fast limiter function (the sense resistor could turn on a Vbe and the transistor collector could shunt away gate current from the FET).
      
 
      If fairly accurate and/or variable current control is of interest, one might consider an LT1970-based circuit.
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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