Products Mentioned

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...
Datasheet
LT3045 on Analog.com

Thread Details

  • State Verified Answer
  • Replies 2 replies
  • Subscribers 39 subscribers
  • Views 444 views
  • Users 0 members are here
Related Content

        

            Post
             Go back to editing
        

    

    


    

    









		


















	
	
			
	
			
		
	
	
		

	    
	    
	    		
Dropout Voltage and Programmable Current Limit

		
	
				

			

									
					    ThomasSL
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Mar 31, 2026 
				
			
			
		

		
		                     
				
        		

		    
		    		    

		      		            		        
Category: Hardware

    		        		            		    
Product Number:  LT3045  

    		        		    		    

		    		    
		    			

			    


The dropout voltage with an input voltage of 15V at ILOAD = 300 mA (300mV) and 500 mA(430mV) appears to be too high in our measurements. We measured Input und Output voltage and calculated the dropout voltage like that.


Circuit Design: (Rlim = 0ohm, 4,7uF on Input Voltage)
 




Additionally, we would like clarification on the correct method for measuring the programmable current limit of the LT3045.


According to the datasheet, the current limit is specified with VIN = 2 V and VOUT = 0 V.
 Our understanding is that the measurement should be performed as follows:


    

  1. Apply VIN = 2 V to the LT3045.
    2. 

  2. Connect a load to the output.
    3. 

  3. Increase the load current gradually.
    4. 

  4. The point at which the output current stops increasing—while the output voltage begins to drop—should correspond to the current limit.
    5. 



Could you please confirm whether this is the correct method for measuring the programmable current limit?



			

			
									
		                                 
Thread Notes  

                

        
                                        
                        

    

                                            
                 hardware
                
                                                    
                 lt3045
                
                                                    
                 LDO Linear Regulators
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			


				
	









	
    
	

  • 
	
    



	
			
		
	



    
	
    
		
    
							
					
    
		
    
		    
		    		    
			
				
									
							        
			
			
			
    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Apr 2, 2026 4:28 AM
            
            
						
			            		
    
		
										0
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    Hello,
     
    The values you get for the dropout is aligned to the datasheet, please see page 3 under Dropout Voltage parameter. 
     
    Yes this is the correct way to measure and check the current limit. Another way is if you are using a resistor at ILIM pin, you can measure the voltage drop across which will be in the range of 0V to 300mV and calculate the equivalent current. This pin is also use for current monitoring, see datasheet page 20.
     
    Thanks.
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
				
				
				
		
		
    
			
		
    
	
    

    

    • 

	

  • 
	
    



	
		
	
	



    
	
    
		
    
							
					
    
		
    
		    
		    		    
			
				
									
							        
			
			
			
            
						
                            
            
            				
            
                on Apr 9, 2026 8:12 AM
            
            
						
			            		
    
		
										0
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    Thank you for the information.
    I measured the dropout voltage as described in the Note 5 from the datasheet. However, the soft dropout voltage is still to high with 314mV for the 300mA Load and 429mV for the 500mA Load. 
    

    I measured it like that:
    

      

    • Set the desired load current (e.g., 300 mA or 500 mA).
      • 

    • Apply a sufficiently high input voltage so the LDO is fully regulating (e.g., 2–3 V above Vout).
      • 

    • Measure the regulated output voltage at this load → call this Vout_reg.
      • 

    • Calculate the 1% regulation limit:

      Vout_1%= 0.99×Vout_reg
      

      • 

    • Slowly reduce the input voltage (VIN) until the output drops to Vout_1%.
      • 

    • At that moment, record VIN → call it VIN_reg.
      • 

    • Dropout voltage = VIN_reg – Vout_1%.

      The programmable current limit works. Thank you!
      • 

    

    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

    •