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The error of converting for AD7657



		

			

									
						Kaos
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on Jun 21, 2013 
				
			
			
		


				
		

		    		    
		    
		    	
			
Dear Sir/Madam,

 
I am studying to design with your 12 AD7657s that have same lot number.

 
So I met the error problem.

 
Why is this trouble happen?

 
Please give me your good advice reason why?

 
Condition:

 
When I input 10V dc here, your AD7657 converted the result 8111 to 8131digit.

 
This have higher 50 or 60 digit than a theoretical value.

 
Also input -10V dc here, the converted result was -8111 to -8131 digit.

 
And when I put this on high tempereture area, the convert value have higher around 100 digit than a theoretical value.

 
Of cource AD7657 have the positive full scale error +/-0.61%.

 
This means 2^14 * 0.0061=99digit, correct?

 
If so, 50 or 60 digit means within the full scale error, and no problem correct? 

 
In this case, the reason why is come from Vref drift, I thought.

 
But Vref come from extrnal source and stable.

 
At in front of analog input(T/H AMP), there is a buffer OPAMP as voltage follower such as your good OP07.

 
Thanks Kaos