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LTC2485 Production
The LTC2485 combines a 24-bit plus sign No Latency ?S™ analog-to-digital converter with patented Easy Drive technology and I2C digital interface. The patented...
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LTC2485 on Analog.com

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LTC2485: can it be used for shunt high side measurement?



		

			

									
					    VictorCanoz
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Apr 22, 2020 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hello,
    

    I would like to use the LTC2485 for directly measuring a high side shunt voltage for measuring a highly dynamic current.
    

    The shunt resistance will be 30 ohms and the voltage after the shunt will be regulated (to compensate for the shunt variable drop). 
    

    So the VIN+ and VIN- signals will not correspond to a fully differential signal, because VIN- will be kept at a relative constant voltage whereas VIN+ can go up to 1.6V from VIN-. Therefore the middle voltage will be changing, possibly at a high frequency.
    

    So my questions are:
    

      

    1. Is this ADC recommended for this kind of measurement? If not, what can you recommend?
      2. 

    2. Is there any drawback in accuracy compared to a properly centered fully differential signal?
      3. 

    3. The input signal will contain high frequency content, so I plan to use a double 10kOhms 1nF RC antialiasing filter before the inputs, is this OK?
      4. 

    

    Many thanks,
    

    Victor
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                        
                on May 1, 2020 10:26 PM
            
            
					
      
	
      

		
		
      
					
      Hi Victor,
      

      The LTC2485 has a very slow conversion rate. To measure the current of a rapidly changing signal, a SAR converter such as the LTC2512-24 might be more appropriate. The LTC2512-24 has a wide common mode range, so it is not necessary to worry about the relation of VIN+ to VIN- as long as both inputs stay between ground - 0.3V and Vref + 0.3V. The recommended input filter is 10ohms and 6800pF. This allows the inputs time to settle after each sampling glitch. If not run at the maximum sampling rate of 2Msps, the filter can be increased.
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
				
						
				
				
		
		
      
			
		
      
	
      

      

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      •  Analog Employees  
      
            
			                            
                        
                on May 1, 2020 10:26 PM
            
            
					
      
	
      

		
		
      
					
      Hi Victor,
      

      The LTC2485 has a very slow conversion rate. To measure the current of a rapidly changing signal, a SAR converter such as the LTC2512-24 might be more appropriate. The LTC2512-24 has a wide common mode range, so it is not necessary to worry about the relation of VIN+ to VIN- as long as both inputs stay between ground - 0.3V and Vref + 0.3V. The recommended input filter is 10ohms and 6800pF. This allows the inputs time to settle after each sampling glitch. If not run at the maximum sampling rate of 2Msps, the filter can be increased.
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
				
						
				
				
		
		
      
			
		
      
	
      

      

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