Products Mentioned

AD7175-2 Recommended for New Designs
The AD7175-2 is a low noise, fast settling, multiplexed, 2-/4- channel (fully/pseudo differential) S-? analog-to-digital converter (ADC) for low bandwidth...
Datasheet
AD7175-2 on Analog.com

Associated Drivers

AD7172-2 Recommended for New Designs
TThe AD7172-2 is an intelligent, low noise, low power, multiplexed, S-? analog-to-digital converter (ADC) with 2- or 4-channel (fully differential/single...
Datasheet
AD7172-2 on Analog.com

Associated Drivers

AD7177-2 Recommended for New Designs
The AD7177-2 is a 32-bit low noise, fast settling, multiplexed, 2-/4-channel (fully/pseudo differential) S-? analog-to-digital converter (ADC) for low...
Datasheet
AD7177-2 on Analog.com

Associated Drivers

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Questions about AD7172/5/7-2



		

			

									
					    HAW
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Nov 14, 2016 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I have questions about AD7175-2, but I beleive they would also valid for AD7172-2 and AD7177-2, so the answers would be relevant for their users too.
    
 
      
  
    1. May the inputs be shared between the channels? E. g if Ain0 and Ain1 set up for differntial measurement on channel 0, may the Ain1 be used for single ended measurement on channel 1?
      2. 
  
    2. I am a bit confused about dat rate and channels. if the data rate is 100 SPS, would it mean 50 SPS effective rate with 2 channels?
      3. 
  
    3. For the reason of simplicity the ADC is to be used to measure following signals with full scale voltages:
      4. 
 
    
 
      
  
    1.  +/- 1 V bipolar differential signal. (eg channel 0) 
      2. 
  
    2. 5 V unipolar pseudodifferintal (channel 1)
      3. 
 
    
 
    The b) forces to use 5 V external refernce, which is disadvantageous for measurement on channel 1. Luckily, the ADC has inetrnal 2.5 V reference, which could be used on channel 1 to bring it closer to optimum range. Would it make sense to do so?
    
 
    I may have further questions as I move on with the programming.
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 Multiplexed A/D Converters
                
                                                    
                 ad7177-2
                
                                                    
                 ad7175-2
                
                                                    
                 Precision A/D Converters
                
                                                    
                 ad7172-2
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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                on Nov 17, 2016 7:18 AM
            
            
					
        
	
        

		
		
        
					
        Hi Jellenie
        
 
        6 b) I made an error in the formulation of the original question. I meant to ask what happens to analog inputs (that are assigned to a channel) between sampling? In which state are they?
        
 
        The ADC is going to be used in test & measurement of the lithium batteries, some of them as small as 10 µAh with charging/disharging currents down to 1 µA. The currents into the ADC could manifest as unaccounted charging/discharging currents. Thus it is crucial to exactly understand what currents at which moments of time are flowing to the ADC, which   is  the purpose of Q6 in conjunction with Q4. For example I guess that the  30 nA is the current during sampling, and it should be significantly less when the mux is open. But that exactly the problem that I have to guess. 
        
 
        I need to know for sure and kindly ask to answer the questíons 4 and 6 b) as precise and detailed as possible.
        
 
        Thanks
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Nov 17, 2016 7:18 AM
            
            
					
          
	
          

		
		
          
					
          Hi Jellenie
          
 
          6 b) I made an error in the formulation of the original question. I meant to ask what happens to analog inputs (that are assigned to a channel) between sampling? In which state are they?
          
 
          The ADC is going to be used in test & measurement of the lithium batteries, some of them as small as 10 µAh with charging/disharging currents down to 1 µA. The currents into the ADC could manifest as unaccounted charging/discharging currents. Thus it is crucial to exactly understand what currents at which moments of time are flowing to the ADC, which   is  the purpose of Q6 in conjunction with Q4. For example I guess that the  30 nA is the current during sampling, and it should be significantly less when the mux is open. But that exactly the problem that I have to guess. 
          
 
          I need to know for sure and kindly ask to answer the questíons 4 and 6 b) as precise and detailed as possible.
          
 
          Thanks
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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