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AD5290YRM250: Strange effects

Question asked by riscy0000 on Apr 11, 2017
Latest reply on Jun 29, 2017 by musach

I have attached 3 wire SPI bus AD5290YRM250 and AD5290YRM2100 (50K and 100K). The device is powered by +5V and DGND.

 

I have attached VA = 4.096V, W attached to comparator (removed for test) and 1uF/18nF cap to DGND, VB to DGND. It used to set threshold to comparator input but that is removed for measurement below.

 

I have checked pin layout and SPI bus timing and see no violation.

 

VW(expected) = DATA * 0.016mV

 

INSERT DATA         VW (actual)      VW(expected)

93                              1495           1488

118                             1877          1888

125                           1967            2000

131                           1979            2096

137                           1963            2192

143                           2046            2288

150                           2060            2400

156                           2244            2496

162                           2773            2592

168                           2800            2688

175                           2898            2800    

187                           2967            2992

218                          3455            3488

237                           3756           3792Excel chart

 

Please advise what I have done wrong here?

 

Tested on 50K and 100K pot with same results.

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