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ADS8681: Resistance drawn in Figure 102 :"Board Layout for the ADS868x"

user5978507
Prodigy 30 points

Part Number: ADS8681

When we look at the layout diagram of Figure 102, the resistors are located between REFCAP and 10uF, REFIO and 4.7uF.
Please tell me the role of this resistors, and recommended resistance value.











								


				
				

				
			

		

			
						
									
                			    			            
						
						
			
			
			
			                        
			

				

			


			

		


				    			

						

















	

	

					
    
	
    





		
	
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                          TI__Mastermind
                        47835 points
                      
    
                          
                   		
		
    
					
    Hi user5978507,
    

    The large value capacitors on both pins can affect the stability of the internal amplifier on the device, therefore it is recommended to use a series resistor to isolate the amplifier output and make it more stable. The value of resistor is dependent on the output impedance of the driving amplifier as well as on the signal frequency. Typical value of resistor range between 0.1 Ω to 2 Ω and the exact value can be found by using SPICE simulations. It is recommended to use the smallest possible values to avoid any voltage spikes at the reference pin, which can potentially affect the conversion accuracy. On ADS8681EVM board, I used 0.47Ω resistor on REFIO pin and 0.22Ω resistor on REFCAP pin, the ADC worked well and the measured performance fulfilled the specifications in ADC's datasheet. I hope this information is helpful to you.
    

    Regards,
    

    Dale
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                 	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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						in reply to Dale Li
					
									
    
	
    
	                                    
                      
    
                        
                          Prodigy
                        30 points
                      
    
                          
                   		
		
    
					
    Hi Dale,
    

    Thank you for your reply.
    

    This reply solved my question.
    

    Best regards,
    

    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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