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AD7656YSTZ conversion error

Question asked by wss on Dec 27, 2016
Latest reply on Jan 9, 2017 by jcolao

AD7656YSTZ has been used in a prototyping board with V1 (pin 33) input a triangle wave 20mVpp at 1Hz. However, the result got from ADC DOUTA (pin 7) is clipped triangle wave instead.

The prototyping card with ADC configured as:
(1) Pin 1 (REFBUFEN/DIS) pin is configured to Logic 1 to disable the internal reference buffers
(2) Pin 10 (HBEN/DCEN) pin is configured to Logic 0 (DGND) which operate in serial mode but not in daisy-chain mode
(3) Pin 27 (Range) pin is configured to Logic 0 (DGND) conversion is ±4 × VREF
(4) Pin 61 (SER/PAR) pin is configured to Logic 1 for serial mode
(5) Pin 63 (REFEN/DIS) pin is configured to Logic 0 (DGND), the internal reference is disabled
(6) SCLK (pin 11) is running at a very low speed.


Question:
(Q1) is there anything wrong with the above configuration?
(Q2) Is there any conversion error with internal ADC?
(Q3) What is the cause?
(Q4) any batch lots issue?

 

attached is the waveform after ADC conversion.

Please kindly advise.

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