Q&A -URGENT- AD7688 analog input is instability.

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-URGENT- AD7688 analog input is instability.

Hiroyuki.D on Sep 20, 2018

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

Top Replies

jcolao
Sep 20, 2018 +2 verified
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…

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+1 jcolao

on Sep 20, 2018 1:28 PM over 2 years ago
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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0 Hiroyuki.D on Sep 21, 2018 10:45 AM over 2 years ago in reply to jcolao

Dear Jonathan

Thank you very much for your reply. I recognize the choice of ADC by mistake.

Regards,

Hiroyuki
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0 Hiroyuki.D on Sep 21, 2018 10:45 AM over 2 years ago in reply to jcolao

Dear Jonathan

Thank you very much for your reply. I recognize the choice of ADC by mistake.

Regards,

Hiroyuki
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