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AD7357 conversion problems

Question asked by vlad_balu on Jun 10, 2013
Latest reply on Jun 17, 2013 by vlad_balu

               Hi. I have a problem with the AD7357 ADC, meaning that each time I ask the device to make a conversion it gives back a different conversion , although it is the same tension at the inputs. It should have returned the same value each time but it varies a lot(even the MSB). I have spotted some potential causes for the problem, but I don't have the necessary experience to deal with them. The possible causes are: at pin3(REFA) there is 3.87 V while in the datasheet it says it should be 2.048 (the internal reference). The other problem is with the CS line, which is oscillating a lot, as you can see on the picture that I attached(with yellow is the SCLK, with purple is SDATA, with light blue is the CS line). I also attached a schematic of the ADC circuit.

              Thank you very much. adc7357sch.bmp