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How to calculate value of series resistor on DAC Output of LTC2974?



		

			

									
					    Purvi
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 24, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    		            		        
    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  LTC2974, LT3045 
    
    		        		    		    	
			
    Hi ADI Team,
    

    Can you help us with below query?
    

    For LT3045, how can we derive the value of R30? In datasheet of LTC2974, equations are available to derive these resistor values but considering the situation where R20 is available in design. But in case of LT3045, R20 is not included in design as output voltage can be configured with help of R10 itself.
    

     
    

    Let us know your thoughts
    

    Regards,
    

    Purvi
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
			                            
                        
                on Nov 28, 2022 5:00 PM
            
            
					
      
	
      

		
		
      
					
      Hi Purvi, the general answer to your question can be found in the DC2518 demo manual on pg 16.  I covered the case of managing a 12V rail which is probably a higher voltage than your case.  The concept is similar.  If your Vout voltage needs to be margined over a small range, you need to connect two series resistors from SET pin to GND.  The DAC is tied to the mid point of the resistors. When the DAC moves up/down, this translates directly to movement in Vout.  You don't need R10, R20, or R30.
      

      When driving a SET pin, the DAC should be set to non-inverting mode.
      

      Also you need the SET resistors because the DAC is high Z when the regulator powers up.  The resistors set the initial Vout voltage.
      

      Mike
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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