AD7655 relationship between internal MUX and accuracy


Our customer is measuring accuracy of AD7655 and please let me know your advice relationship between internal MUX and accuracy.

Our test resul shows  large difference  (about 50~100LSB) between channel A (INA1 and INA2) and channle B (INB1 and INB2).

So, he has verified as below .

Input: AGND

Power supply: 5V

REF: AD1582

Interface: test  using both SPI and parallel

Number of test: 500  ( test is 2pattern which remains A0 = low  or high )

Sample: 3 samples

Test  result is below

Channle A (IINA1 and INA2) : about  100LSB +- 10LSB

Channle B (INB1 and INB2) :almost 0LSB

( for your information,  

in the case of input 1.0V ,  ( output of ADA4666-2 voltage follower is connected to INA1, INA2 , INB1 and INB2) ,

channle A  = 13296LSB (averaged value for 500 time),

channelB = 13230LSB (averaged value for 500 times)

I think that the internal difference between Channel A and B is internal MUX of AD7655.

Does internal MUX affect converted result as above  ?

I would like to know if above appearance is in specifaication or AD7655 characteristcs .

And we are checking his circuit design , layout and timing diagram.

Please let me know your advice



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