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ADP1741ACPZ-R7 dropout voltage



		

			

									
						Belenie
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on Jan 27, 2015 
				
			
			
		


				
		

		    		    
		    
		    	
			
Hello,

 
For analog Devices ADP1741ACPZ-R7 the datasheet specifies the dropout voltage for conditions when Vout is 1.8V or higher as 280mV max on page 3 (although footnote 4 actually says for when Vout is 1.6V or higher). The datasheet also shows the dropout voltage verses load current for both Vout = 1.6V and Vout = 2.5V in Figure 12 on page 8.

 
 

 
In my application, my Vout = 1.3V and I would like to know what my dropout voltage is @ 2A. It would be nice to see a graph as shown in Figure 12 but I would be happy with just knowing the worst case dropout with Vout = 1.3V and 2A load current.

 
 

 
Thanks,

 
Belenie 

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	










	

	

					



			








	
	
	
	



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                                 Analog Employees 
                                
                            
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                on Feb 5, 2015 3:38 AM
            
            
					
    
	
    

		
		
    
					
    Hi Belenie,
    
 
    You could use a headroom below 400mV but that would depend on how much noise is going in to the ADP1741 and how much noise is allowed to come out of it. With low headroom the effective drain to source voltage of the pass element is equal to VDS = VIN – VOUT - VDO, this means that the pass element of the LDO is operating in the linear region instead of the saturation region and you effectively have a resistor that does not filter any noise in your input. Long story short, the lower the headroom the lesser is the filtered noise. However if you have a clean input for the ADP1741, you could run it below 400mV but we still recommend that you use the 400mV headroom.
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
						
						
				
				
		
		
    
			
		
    
	
    

    

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													0
							
			
				
									
							        
            
                                                                                                        
      
                            
    • 
                                 Analog Employees 
                                
                            
      • 
                        
     
                                                           			
			                            
                        
                on Feb 5, 2015 3:38 AM
            
            
					
    
	
    

		
		
    
					
    Hi Belenie,
    
 
    You could use a headroom below 400mV but that would depend on how much noise is going in to the ADP1741 and how much noise is allowed to come out of it. With low headroom the effective drain to source voltage of the pass element is equal to VDS = VIN – VOUT - VDO, this means that the pass element of the LDO is operating in the linear region instead of the saturation region and you effectively have a resistor that does not filter any noise in your input. Long story short, the lower the headroom the lesser is the filtered noise. However if you have a clean input for the ADP1741, you could run it below 400mV but we still recommend that you use the 400mV headroom.
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
						
						
				
				
		
		
    
			
		
    
	
    

    

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