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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
                
                                                    
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                 Precision A/D Converters
                
                                                    
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jan 9, 2013 11:38 PM
            
            
					
      
	
      

		
		
      
					
      Hi Lyn,
      
 
      Adding diodes such as schottky diodes from the analog input pin to AVDD and AGND will protect the AD7739 against overvoltages.
      
 
      Regarding the analog input range of the AD7739, the device can accept an analog input of +/-2.5V. The device operates from a single power supply so the analog input must be biased up. For example, if the voltage on AIN+ swings from 1.25V to 3.75V and the voltage on AIN- is 180 degrees out of phase, then the voltage AIN+ - AIN- = 3.75V-1.25V = 2.5V when AIN+=3.75V and AIN-=+1.25V. When AIN+=1.25V and AIN-=3.75V, the voltage AIN+ - AIN- = 1.25V – 3.75V = -2.5V. So, the ADC sees an analog input of +/-2.5V. However,please ensure the voltage on AIN+ and AIN- is between 0.2V and AVDD – 0.3V as per the spec for the absolute voltage on AIN+/AIN- on table 1 in page 3 of the datasheet. 
      
 
      About the input to the instrumentation amplifier, what magnitude and frequency are you using?
      
 
      We have parts like the AD7190 that features an on-chip PGA with gains of up to 128 and an output data rate of up to 4.8kHz. You might find this helpful in your application.
      
 
      Hope this helps.
      
 
      Thanks and Best Regards,
      
 
      Chris
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jan 9, 2013 11:38 PM
            
            
					
      
	
      

		
		
      
					
      Hi Lyn,
      
 
      Adding diodes such as schottky diodes from the analog input pin to AVDD and AGND will protect the AD7739 against overvoltages.
      
 
      Regarding the analog input range of the AD7739, the device can accept an analog input of +/-2.5V. The device operates from a single power supply so the analog input must be biased up. For example, if the voltage on AIN+ swings from 1.25V to 3.75V and the voltage on AIN- is 180 degrees out of phase, then the voltage AIN+ - AIN- = 3.75V-1.25V = 2.5V when AIN+=3.75V and AIN-=+1.25V. When AIN+=1.25V and AIN-=3.75V, the voltage AIN+ - AIN- = 1.25V – 3.75V = -2.5V. So, the ADC sees an analog input of +/-2.5V. However,please ensure the voltage on AIN+ and AIN- is between 0.2V and AVDD – 0.3V as per the spec for the absolute voltage on AIN+/AIN- on table 1 in page 3 of the datasheet. 
      
 
      About the input to the instrumentation amplifier, what magnitude and frequency are you using?
      
 
      We have parts like the AD7190 that features an on-chip PGA with gains of up to 128 and an output data rate of up to 4.8kHz. You might find this helpful in your application.
      
 
      Hope this helps.
      
 
      Thanks and Best Regards,
      
 
      Chris
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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