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LT3086 Output Below 400mV



		

			

									
					    RobertDS
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Feb 12, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I'm using the LT3086 as a linear postregulator to a switching power supply. I'm designing a circuit that acts like an adjustable power supply for a bench. I had planned on using LTC7106 to adjust the output voltage of the LT3086 and the switcher. If I were to inject more than 50uA into the SET pin, would I be able to drive the LT3086 output all the way down to 0V (given the appropriate current for the SET resistor)? 
    

    Prototype test circuit excerpt below:
    

    

     
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                        
                on Feb 23, 2021 4:33 PM
            
            
					
      
	
      

		
		
      
					
      I just tried driving OUT to 0V using LTspice and the method you describe but the output did not go all the way to 0V.  I show the simulation circuit and results in the image below and I uploadedLT3086_Andy_1.asc my LTspice circuit.
      

      

      sim ckt and results_1.png
      

      

      

      

      

      

      

      

      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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                on Mar 2, 2021 2:24 PM
            
            
												
						in reply to ARad
					
									
        
	
        

		
		
        
					
        The sim only draws extra current from the pin to adjust the voltage up. You'd need to inject more than 50uA into the SET node to pull the voltage to ground.
        

        I tweaked the simulation to do that (replaced voltage source with current source that ramps from 0 to 55u, then down to -55u) and the regulator seems to go to ground subject to the load discharging the output. The sim implies a nonlinear recovery right when the output starts to rise again from 0V, but it appears minimal.
        

        (I'm having an issue uploading a screenshot of this. "Insert image" is requiring a URL, and not showing a file upload button)
        

        Would there be any other issues beyond a small control loop recovery transient?
        

        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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													0
							
			
				
									
							        
			
			
			
          
            
			                            
                        
                on Mar 2, 2021 2:24 PM
            
            
												
						in reply to ARad
					
									
          
	
          

		
		
          
					
          The sim only draws extra current from the pin to adjust the voltage up. You'd need to inject more than 50uA into the SET node to pull the voltage to ground.
          

          I tweaked the simulation to do that (replaced voltage source with current source that ramps from 0 to 55u, then down to -55u) and the regulator seems to go to ground subject to the load discharging the output. The sim implies a nonlinear recovery right when the output starts to rise again from 0V, but it appears minimal.
          

          (I'm having an issue uploading a screenshot of this. "Insert image" is requiring a URL, and not showing a file upload button)
          

          Would there be any other issues beyond a small control loop recovery transient?
          

          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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