Resolution and INL problem in AD5791

Dear all,

I m facing a problem with the use of the ad5791 evaluation board.

In fact, with this card I'm supposed to get an output voltage resolution of 1 LSB ( 20 µV), instead of this ,  when I increment the the 20 bit word with 1 LSB, nothing happens at the output voltage ,

The output voltage is updated only with 3 increments ( 3LSB = 60 µV) .

On the other hand, the INL error is indicated in the AD5791 datasheet to be less than 1 LSB. Here again, in our experiment and using the evaluation board its value is greater than 3lsb (60 µV)

Please Find attached the screen shot of the INL and the resolution steps we measured.

Could you please give me some helps , It will be appreciated.

Thank you

attachments.zip
    •  Analog Employees 
    on Jul 7, 2016 6:47 AM over 4 years ago

    Hi,

    Would you be able to provide the sweep of codes and the corresponding voltages (excel sheet, or csv)? I am trying to understand the graphs that you have on your first post. Would you kindly explain how did you came up with those graphs? Also, if you wouldn't mind, what is setpoint that is measured in volts and temps on the second graph? Also, how are you computing for the INL?

    Regards,

    Mark

  • Hi,

    Please find attached the excel sheet of the sweep of codes and the corresponding voltages that will clarify how I computed the INL and how I got the excel graph. For the labview graph, I used the 3458A Agilent multimetre to acquire the voltage values.

    I did the test by generating a step values of one LSB (20 uV) and thus generate voltage ramp as shown in the Labview figure. The INL is then obtained by substracting the voltage measured using the multimeter from the setpoint voltage.

    Please feel free to contact me if you need any further information.

    Regards.

    Excel sheet.xlsx - Google Drive

  • Could you please give me the configuration of the "Control Register" used by the AD program ??

    regards,

    joseph