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AD7998 instable conversion results

Question asked by antonio64 on Nov 28, 2014
Latest reply on Dec 18, 2014 by mayp

Hello,

I am testing the AD7998 on several identical boards. I get 50 samples each second and provide the average of these conversion data.

VREF is provided by REF195. The input data are buffered and filtered and perfectly stable (measured with a precision voltmeter)

On some boards the ADC data is perfectly stable and repeatable at each powerup.

On other boards the conversion results float slowly every 3-4 sec in a range of 10 ADU 

On other boards after power-up with stable input the conversion results starts from different values (also 100 ADU far from the stable value) and reach a stable value after some seconds (also a minute).

I am reading the data after 5us the falling edge of CONVST.

 

Any suggetsions?

Thanks

Antonio

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