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AD7739 Production
The AD7739 is a high precision, high throughput analog front end. True 16-bit p-p resolution is achievable with a total conversion time of 250 µs (4 kHz...
Datasheet
AD7739 on Analog.com

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AD7739 AIN Protection



		

			

									
					    Lyn
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Dec 25, 2012 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    The AD7739 datasheet states that the device can operate with +/- 2.5 volt inputs.
    
 
    The Absolute Maximum ratings for the AIN pins are listed as -0.3V to AVDD + 0.3V which would appear to contradict the input voltage range.
    
 
    I wish to use the device with an external instrumentation amplifier operating with supplies of ca +/- 15V and a ouput voltage range of +/- 2V in normal operation.
    
 
    How should I protect the input of the AD7739 from overvoltage ouput of the instrumentation amplifier.
    
									
			        
		
    

				
						
        

    
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                 Multiplexed A/D Converters
                
                                                    
                 ad7739
                
                                                    
                 Precision A/D Converters
                
                                                    
                 protection
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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                on Jan 10, 2013 2:28 PM
            
            
					
        
	
        

		
		
        
					
        Dear Chris
        
 
        Thank you for your reply. When I printed out the data sheet and studied it more carefully, I realized that the analogue input specification of +/- 2.5 V was for a differential input.
        
 
        The signals I am dealing with are very low frequency with a sample rate the order of 1 second or more so the dynamic performance is not really an issue. The signals have a range of +/- 2V so using an Instrumentation amplifier with a gain of one, I end up with a signal of +/- 2V from whatever reference I choose. I can obviously divide signal by a factor of two and use an ADC with an input range of 0 - 2.5 V, but this is not attractive as I will require eight precision dividers.
        
 
        My conclusion is that I am better off using an ADC with a +/- 2.5 input such as the ADS1258 or with an input range of 0 - 5V with an offset reference.
        
 
        Please let me know if you have any better ideas.
        
 
        Yours sincerely
        
 
        Lyn Roberts
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Jan 10, 2013 2:28 PM
            
            
					
          
	
          

		
		
          
					
          Dear Chris
          
 
          Thank you for your reply. When I printed out the data sheet and studied it more carefully, I realized that the analogue input specification of +/- 2.5 V was for a differential input.
          
 
          The signals I am dealing with are very low frequency with a sample rate the order of 1 second or more so the dynamic performance is not really an issue. The signals have a range of +/- 2V so using an Instrumentation amplifier with a gain of one, I end up with a signal of +/- 2V from whatever reference I choose. I can obviously divide signal by a factor of two and use an ADC with an input range of 0 - 2.5 V, but this is not attractive as I will require eight precision dividers.
          
 
          My conclusion is that I am better off using an ADC with a +/- 2.5 input such as the ADS1258 or with an input range of 0 - 5V with an offset reference.
          
 
          Please let me know if you have any better ideas.
          
 
          Yours sincerely
          
 
          Lyn Roberts
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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