-URGENT- AD7688 analog input is instability.

Question

Hi 
 We're facing a issue that the analog input is instability below. 
 
 CH4 is IN+. CH3 is SDO. 
 Actually the driver amp is OPA197 (Ti), we recommend ADA4084-1 instead of Ti. 
 But the customer say if the instability is not improved within this week, he may use ADS8863 (Ti) instead of AD7688. 
 The input+ is DC voltage and the input- is GND as single input. 
 Could you please give me any advice. 
 Thank you very much in advance. 
 OPA197 
 http://www.ti.com/product/OPA197?keyMatch=OPA197&tisearch=Search-EN-Everything 
 ADS8863 
 http://www.ti.com/product/ADS8863?keyMatch=ADS8863&tisearch=Search-EN-Everything 
 
 Regards, 
 Hiroyuki

jcolao · Accepted Answer

Hi Hiroyuki, 
 The customer is having Vin+=DC voltage and Vin-= GND. What is the value of the DC voltage? This should work if Vin+= Vref. Please take note that the AD7688 is a differential ADC, it is expecting that the input of Vin+ and Vin- is opposite with each other and also take note of common mode voltage Vref/2, which means the difference of the Vin+ and Vin- should be within the common mode voltage. 
 The customer may use AD7686, which is a Pseudo Diff ADC basing from the input voltage that you mentioned. 
 
 Regards, 
 Jonathan

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-URGENT- AD7688 analog input is instability.

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