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LT3042 Recommended for New Designs
The LT3042 is a high performance low dropout linear regulator featuring LTC’s ultralow noise and ultrahigh PSRR architecture for powering noise sensitive...
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Adding trimming capabilities for LT3042 output voltage

		
	
				

			

									
					    MaxHolden
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on May 23, 2025 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  LT3042  
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hello,
    

    I would like to use the LT3042 to generate a low noise ( <10uVRMS at BW 10Hz->100kHz) rail of 2.5V nominal with +-200mV trimming capability (2.3V to 2.7V).
    

    I was thinking of implementing the circuit by using a 22.9kOhm 0.1% (2.29V output) precision resistor in series with a 470Ohm multiturn trimmer used as a variable resistor
    

    My main doubts with this solution are:
    

      

    1. The poor charateristic of the pot will introduce too much noise and instability (TC)
      2. 

    2. It becomes more difficult to guard the SET signal on the PCB due the big size of potentiometer and it will for sure degrade noise perfomarce
      3. 

    

    The second implementation i tought of is by using an external reference that has TRIM capabilities (like MAX6225) but the range is usally smaller (+- 25 or 50mV)
    

    Thanks for the help.
    
			
    
			
									
		                             
                        

    
    
                                            
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jun 3, 2025 12:38 PM
            
            
						
			            		
      
		
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      Are you expecting to manually adjust the voltage, or would you like a digital interface? You can use a DAC to force around the SET voltage for the latter.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
				
				
				
		
		
      
			
		
      
	
      

      

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                on Jun 9, 2025 3:50 AM
            
            
												
						in reply to RDSmith
					
										
			            		
        
		
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        I prefer to manually adjust the voltage because i don't have any MCU or PC available to control a digital ICs like DAC or digipot.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        
            
						
                            
            
            				
            
                on Jun 9, 2025 8:44 AM
            
            
						
			            		
        
		
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        I think that, if you're putting a trimmer potentiometer in the circuit, if you put it on the low-side of the series pair (resistor connected to SET pin, then pot connected to resistor), you should only need to guard the resistor area, as if you guard the potentiometer you will . You could add filtering capacitors to the potentiometer to help with noise, so long as they are low-leakage (like a small ceramic NP0 / C0G capacitor). As for the temperature coefficient, unfortunately don't have a good recommendation. If the pot has a positive temperature coefficient, you might be able to balance it with something that has a negative temperature coefficient (like a diode), but the extra shift in voltage will likely be unacceptable.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
						
				
				
				
		
		
        
			
		
        
	
        

        

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