Questions about AD7682

Hi,
   I am using AD7682 to make a data aquisition system.
   I connected the COM(pin10) to GND and used the internal reference 2.5V.
   But when the amplitude of the input sinewave exceed about 1.2V, half of the reference voltage, it seemed that the waveform ploted according to the converted result not exactly the right.
   Why it performs like this?
   By the way, the input signal composed of about 600mV DC offset and a sinewave about 600-700mV peak to peak?
   When I used the internal 4.096V reference, should the input voltage below about 2V? Or it could be 4.096V?
   Thank you!

  • 0
    •  Analog Employees 
    on Jan 11, 2012 9:48 PM

    Hi-

    I moved this question about the AD7682 to the Precision ADCs community.  Please continue the discussion here.

    Thanks,

    AndyR

    EngineerZone Community Manager

  • 0
    •  Analog Employees 
    on Jan 12, 2012 12:33 AM

    Hello Keven,

    All AD7682 input channels, IN[7:0], can be referenced to a common-mode point of 0 V or VREF/2 V for COM input pin 10. The max absolute CM input voltage is VREF/2 + 0.1V when using any reference voltage option. So, if you try to go beyond this limit, the part may not work properly.

    Make sure that you have followed the decoupling guideline from the datasheet. A 10uF (X5R, 1206 size) ceramic chip capacitor is appropriate between the REF and GND pins. The REFIN pin can be decoupled with a 0.1uF capacitor.

    Regards,

    Maithil

  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:32 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin