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Using a LT1999 for unidirectional current sense



		

			

									
					    GlennM
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 1, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  LT1999-50 
    
    		        		    		    	
			
    I have a need for a multipurpose current sense amplifier. Our current circuit uses a LT1999-50 and works fine using the reference voltage generated from the chip, 
    but we are trying to combine designs where another current sense is not bidirectional. Is it OK to ground the REF pin to use the full range of the output of the device in a unidirectional fashion?
    Due to supply chain issues our choices are small, but if there is a recommendation to use another device that would be fine as well, but at this point I would really like to know if the REF pin can be grounded.
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
			                            
                        
                on Nov 2, 2022 8:39 AM
            
            
					
      
	
      

		
		
      
					
      Hi,
      

      Moving this to the amplifiers community.
      

      Thanks,
      

      Kristine
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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      •  Analog Employees  
      
            
			                            
                        
                on Dec 5, 2022 3:13 AM
            
            
					
      
	
      

		
		
      
					
      Hello Glenn,

      I would not recommend connecting the REF pin to ground.
      From the datasheet, there is a specification for REF pin voltage input range. This range ensures that the part does not heat up outside the full operating temperature range.
      Now if you check the internal circuit connected to the REF pin, you will see that the REF pin is internally connected to the supply voltage and ground through 160kohm resistances.
      If you connect the REF pin to ground, then the supply voltage will then be connected to ground through just a 160kohm resistance (instead of 2 160kohm in series) which will then generate a larger current through it.
      A larger current could heat up the part, so operation is not guaranteed.

      Is the range of one direction of the bi-directional LT1999 not enough for your application?

      Best Regards,
      Sham


      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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