Products Mentioned

LT3092 Production
The LT3092 is a programmable 2-terminal current source. It requires only two resistors to set an output current between 0.5mA and 200mA. A multitude of...
Datasheet
LT3092 on Analog.com

Thread Details

  • State Verified Answer
  • Replies 5 replies
  • Subscribers 41 subscribers
  • Views 1198 views
  • Users 0 members are here 

        

            Post
             Go back to editing
        

    

    


    

    









		


















	
	
			
	
			
		
	
	
		

	    
	    
	    		
LT3092 monitor Vout

		
	
				

			

									
					    KP3
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Dec 10, 2025 
				
			
			
		

		
		                    	    

        	    
Thread Summary

                The user is designing a circuit to monitor leak detection in a 4-wire cable using the LT3092 to pass a constant 1.01mA current. A voltage divider (R6 and R7) is added to detect if the cable is connected. The voltage divider has a negligible effect on the current output (changing it by about 1nA). Vout will be 12V when the cable is disconnected and will depend on the cable's resistance when connected (1310 Ohms for a 100-meter cable).
                        	    

                
                     AI Generated Content
                
    	    

             
				
        		

		    
		    		    

		      		            		        
Category: Hardware

    		        		            		    
Product Number:  LT3092  

    		        		    		    

		    		    
		    			

			    
Hi ADI Team,

I am currently designing a circuit to monitor a leak detection of a 4 wire cable cable. To do this I am planning to pass a constant 1mA current to the cable using the LT3092 and then convert the resistance of the cable to voltage.
I would like also to detect of the cable is actually connected on the terminal. 

Following is my schematics. The circuit is set to output  1.01mA. 

In have placed an additional voltage divider using R6 and R7 to detect if the cable is connected or disconnected. My question is if this voltage divider will affect the 1.01mA output . Will the Vout voltage when the cable is disconnected be 12V? And what will be the Vout when the cable is connected? 

 

Thank you.

Best Regards,
Kostas

			

			
									
		                             
                        

    

                                            
                 power management
                
                                                    
                 hardware
                
                                                    
                 Current Sources
                
                                                    
                 LT3092
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			


				
	









	
    
	

  • 
	
    



	
		
	
	



    
	
    
		
    
							
					
    
		
    
		    
		    		    
			
				
									
							        
			
			
			
    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Dec 10, 2025 10:12 AM
            
            
						
			            		
    
		
										0
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    Hi,
     
    Looking at an LTSpice simulation for your design (without knowing the resistance of your cable, so 10 ohms was used as the default), it looks like adding the resistor divider for cable detection has little to no effect on the operation (it changed the current by about 1nA). When the cable is disconnected, the voltage at Vout will be 12V. When the cable is connected, the Vout will depend on the cable's resistance. I will try and attach the LTSpice .asc file so that you can simulate it yourself as well.
     
    Thanks!
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

    • 

	

  • 
	
    



	
		
	
	



    
	
    
		
    
							
					
    
		
    
		    
		    		    
			
				
									
							        
			
			
			
            
						
                            
            
            				
            
                on Dec 10, 2025 10:16 AM
            
            
						
			            		
    
		
										0
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    Hi  ,

    Thank you very much for your prompt response.

    Cable will be 100 meters long. 

    Resistance = 13.1 Ohms per meter
    at 100 meter will be 1310 Ohms

    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

    • 

	

  • 
	
    



	
			
		
	



    
	
    
		
    
							
					
    
		
    
		    
		    		    
			
				
									
							        
			
			
			
    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Dec 10, 2025 10:27 AM
            
            
						
			            		
    
		
										+1
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    Hi,
     
    Thank you for letting me know. I have changed the LTSpice simulation, and will upload it in my following message. With the voltage divider, the Vout voltage differs from the design without it by about 0.1uV.
     
    Thanks!
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
						
				
				
				
		
		
    
			
		
    
	
    

    

    • 

	

  • 
	

    • 

	

  • 
	
    



	
		
	
	



    
	
    
		
    
							
					
    
		
    
		    
		    		    
			
				
									
							        
			
			
			
    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Dec 10, 2025 2:42 PM
            
            
						
			            		
    
		
										0
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    If your cable opens, pin 2 of J2 will increase to around 12V since in that case there will not be enough current to satisfy the LT3092's minimum load requirement.  In other words, the LT3092 will turn off if your cable opens.   If you decrease the overall resistance of your R6,R7 voltage divider enough to satisfy the LT3092's minimum load requirement, then pin 2 of J2 will increase to around 12V - 1.2V = 10.8V when the cable opens.  The images below are from the LT3092 datasheet and show the 1.2V dropout voltage and the minimum load specification.  I agree LTspice is a great way to check operation of your circuit.   
    

    

    LT3092 DS dropout_1.png
    

    

    

    LT3092 DS min load_1.png
    

    

    

    

    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

    • 

	





	
			








	






































     



















		        
        

            
Before You Switch

            
        

        

        

            Switching languages will make ADI Explorer unavailable. Resume your session by switching back to English and reopening ADI Explorer.