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LT3045 Recommended for New Designs
The LT3045 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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LT3045 on Analog.com

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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LT3042 on Analog.com

LT3045-1 Recommended for New Designs
The LT3045-1 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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LT3045-1 on Analog.com

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LT3045 Loop-Gain Measurement: Where Should the Injection Resistor Be Placed?

		
	
				

			

									
					    ARad
					
							

            
            			
				
									
											
			
			
				
  •  Analog Employees  

			
			
			    	
			                    
                
				                on Oct 2, 2026 
				
			
			
		

		
		                     
				
        		

		    
		    		    

		      		            		        
Category: Hardware

    		        		            		    
Product Number:  LT3045 

    		        		    		    

		    		    
		    			

			    
I would like to measure the LT3045 control-loop response and generate a Bode plot using a frequency-response analyzer. What is the recommended way to break the loop for this measurement?
 
 Should a small injection resistor be inserted in series between the output capacitor connection and the OUTS sense pin, with the analyzer connected across that resistor? If so, what resistance range works well without significantly disturbing normal operation?

			

			
									    

			        
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[edited by: ARad at 3:35 PM (GMT -4) on 2 Oct 2026]
				

						
		                             
                        

    

                                            
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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Oct 2, 2026 11:38 AM
            
            
						
			                            
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    Yes. A practical way to measure the LT3045 loop gain is to open the remote-sense path and install an injection resistor between the output-capacitor connection and the OUTS pin. Connect the frequency-response analyzer across this resistor in the analyzer’s normal loop-injection configuration.
    

    A 10 Ω resistor has worked well in the lab, and the exact value is not critical; approximately 10 Ω to 100 Ω should be suitable. The resistor provides a convenient AC injection point while maintaining the LT3045’s normal DC output-sense connection.
    

    Make the measurement with the regulator operating at the intended input voltage, output voltage, load current, and output-capacitor configuration, because these conditions can affect the measured loop response.
    

    I uploaded a schematic that shows the injection resistor and the frequency-response analyzer connection.  I also uploaded the results of the Bode plot.   
    

    

    dc3158a-schematic.pdf
    

    

    

    LT3041 DC3158A 5VIN 3.3VOUT at 500mA_0.pdf
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Oct 2, 2026 11:38 AM
            
            
						
			                            
                     Contains AI Generated Content
                
            		
    
		
										0
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    Yes. A practical way to measure the LT3045 loop gain is to open the remote-sense path and install an injection resistor between the output-capacitor connection and the OUTS pin. Connect the frequency-response analyzer across this resistor in the analyzer’s normal loop-injection configuration.
    

    A 10 Ω resistor has worked well in the lab, and the exact value is not critical; approximately 10 Ω to 100 Ω should be suitable. The resistor provides a convenient AC injection point while maintaining the LT3045’s normal DC output-sense connection.
    

    Make the measurement with the regulator operating at the intended input voltage, output voltage, load current, and output-capacitor configuration, because these conditions can affect the measured loop response.
    

    I uploaded a schematic that shows the injection resistor and the frequency-response analyzer connection.  I also uploaded the results of the Bode plot.   
    

    

    dc3158a-schematic.pdf
    

    

    

    LT3041 DC3158A 5VIN 3.3VOUT at 500mA_0.pdf
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

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