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AD7484 Production
The AD7484 is a 14-bit, high speed, low power, successive approximation ADC. The part features a parallel interface with throughput rates up to 3 MSPS...
Datasheet
AD7484 on Analog.com

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AD7484 REFOUT



		

			

									
					    rjm
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Oct 31, 2016 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
      
  
    1. How much current can I draw from the internal reference (REFOUT)? With REFSEL floating with a 0.1uF cap to AGND, REFOUT drops to 1.9V volts with a 4.7K load (0.5ma). Table 10 says the REFOUT impedance is 1 ohm.
      2. 
  
    2. Fig 10 in the data sheet indicates very flat temperature drift (approximately 2mv) but Table 1 says +/100mv. Please explain this difference. My tests here indicate it’s even worse than that. What typical temperature drift should I expect of the internal reference? Is the drift affected by the REFOUT load?
      3. 
 
    
									
			        
		
    

				
						
        

    
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                 Single Channel A/D Converters
                
                                                    
                 ad7484
                
                                                    
                 Precision A/D Converters
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Nov 7, 2016 6:53 PM
            
            
					
      
	
      

		
		
      
					
      Hi,
      
 
         The AD7484 has a typical spec of 220uA. This is usually the typical current to drive the ADC reference and this is also the typical current the internal reference is driving the ADC. Not enough current to drive the ADC will not have a good conversion result .
      
 
         The specs in Table 1 were gathered with the condition indicated on the upper portion on page 3, that is Vdrive = 2.5 to 5.25 and AVDD/DVDD = 5+/-5% and maximum throughput rate at 3MSPS across Tmin and Tmax. The result, with this conditions, will have a maximum reference error of +/-~100mV. Figure 10 of the datasheet shows 1 data plots at varying temperature, this means that it was gathered at specific condition across temperatures.
      
 
      Regards,
      
 
      Jonathan
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Nov 7, 2016 6:53 PM
            
            
					
      
	
      

		
		
      
					
      Hi,
      
 
         The AD7484 has a typical spec of 220uA. This is usually the typical current to drive the ADC reference and this is also the typical current the internal reference is driving the ADC. Not enough current to drive the ADC will not have a good conversion result .
      
 
         The specs in Table 1 were gathered with the condition indicated on the upper portion on page 3, that is Vdrive = 2.5 to 5.25 and AVDD/DVDD = 5+/-5% and maximum throughput rate at 3MSPS across Tmin and Tmax. The result, with this conditions, will have a maximum reference error of +/-~100mV. Figure 10 of the datasheet shows 1 data plots at varying temperature, this means that it was gathered at specific condition across temperatures.
      
 
      Regards,
      
 
      Jonathan
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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