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LTC2974 current sensing filter



		

			

									
						ramiro.polo@bruker.com
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on May 26, 2020 
				
			
			
		


				
		

		    		    
		    
		    	
			
Hello, 


I'm designing a controlled voltage source for 4 channels using a LTC2974 to control four LT3012 LDOs.


My question it's about current sensing ports. In the datasheet defines how to measure the current with a shunt resistor that includes a filter to avoid the switching frequencies from the used DC/DC converter.


I want to use a LDO regulator, the LT3012, my question is the next:


Can I quit the filtering and use directly the shunt resistor to measure the current using a LDO, or I always need to implement some filtering?


If I need the filter, to which frequency is recomendable to filter for the LT3012 LDO?




Many thanks in advance.

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	














	

	

					



			


				
	









	
    
	

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                                 Analog Employees 
                                
                            
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                on Jun 25, 2020 4:45 PM
            
            
					
    
	
    

		
		
    
					
    Hi Ramiro,
    

    Generally LDOs offer low output noise, and it's possible that you could avoid external RC filters.  If the load current is steady and you are expecting for a stable output current reading, then you will likely see accurate and consistent READ_IOUT values.  The 2974 has internal filtering, noise above 62kHz is attenuated.  Note that the 2974's ADC updates each of the channel's READ_IOUT registers every 190ms.
    

    Also I'd like to mention that you should place the sense resistor inside the feedback loop to avoid droop in Vout. The 3021 is capable of 500mA, and selecting the Rsense value is up to you but I suggest using a 50 milli-ohm Rsense. This will produce good accuracy at full load and also will be accurate down to 10mA. 
    

    Regards
    

    Mike
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
						
				
				
		
		
    
			
		
    
	
    

    

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