Products Mentioned

LTC7871 Recommended for New Designs
The LTC7871 is a high performance bidirectional buck or boost switching regulator controller that operates in either buck or boost mode on demand. It regulates...
Datasheet
LTC7871 on Analog.com

Thread Details

  • State Not Answered
  • Replies 1 reply
  • Subscribers 40 subscribers
  • Views 345 views
  • Users 0 members are here 

        

            Post
             Go back to editing
        

    

    


    

    









		


















	
	
			
	
			
		
	
	
		

	    
	    
	    		
LTC7871 Constant Current into Hard Short

		
	
				

			

									
					    AustinAdee
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 13, 2024 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  LTC7871 
    
    		        		    		    
    
		    		    
		    			
    
			    
    Can the LTC7871 configured as a buck converter in constant current mode operate into a hard short (<10mOhm)?
    

    The DS references a "Current Foldback" graph that doesn't exist.
    

     
    

    Will it have stability problems coming out of a hard short? And can the soft-start be defeated when the short is removed?
    
			
    
			
									
		                             
                        

    
    
                                            
                 Datasheet/Specs
                
                                                    
                 Buck-Boost Battery Chargers
                
                                                    
                 hard short
                
                                                    
                 High Input Voltage Buck Regulators
                
                                                    
                 buck-boost dc/dc converter
                
                                        
                                            
                
                
                                        
                                            
                
                
                                        
                                            
                
                
                                        
                                            
                
                
                                
                    Show More
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

    • 
	
      



	
		
	
	



      
	
      
		
      
							
					
      
		
      
		    
		    		    
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Sep 14, 2024 8:34 PM
            
            
						
			            		
      
		
										0
					
	
      

		
		
      
		
      
                                
                                                            
      
					
      Hello Austin,
      

      I received your message. My comments are below:
      

        

      1. If a short is applied to VOUT which is strong enough to cause VOUT to fall out of regulation and the short is subsequently removed, then VOUT will ramp-up with internal soft-start. The supply will not have stability problems after the short is removed. The internal soft-start can not be disabled.

        2. 

      2. For an LTC7871 supply configured as a constant current buck, the foldback current limit will cause the IOUT to be less than the IOUT programmed by the SETCUR pin if the foldback current limit is the lower of the two. Per the foldback charts inserted below (from page 9 of the D/S), the maximum current sense voltage progressively drops once the VFBLOW voltage falls below 0.4V. Therefore it VOUT is set for 14.0V nominal, for instance, then foldback will occur once VOUT falls below 4.7V. If the LTC7871 is being used to charge an automotive 12V battery, this should not be an issue.
           
         
        3. 

      

       
      

      Best regards,
      

      

      Mike
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
				
				
				
		
		
      
			
		
      
	
      

      

      •