About AD7690 ADC

Dear Sir/Madam,

     We are using the AD7690 High speed ADC for our weigh scale application. The ADC input is giving from the Loadcell. In that we using the ARM7 processor.

In that, we developed the firmware in c language to read the digital counts from AD7690 .

Please see the following conditions which we made in hardware side,

*We are using the CS mode, with 3-wire communication(CNV,SDO and Sclk) without busy indicator.

*We connected the VIO to SDI continuously (5v).

*But, the problem was, we were not receiving Any data from the ADC. We think that there might be a problem within our software program.

     Please give us, desired flow to develope the software for this ADC. Please give us any sample code to develope our application with AD7690.

Thanks and Regards,


  • 0
    •  Analog Employees 
    on Jan 20, 2012 9:31 PM


    I moved this question about the AD7690 to the Precision ADCs community.  Please continue the discussion here.



    EngineerZone Community Manager

  • 0
    •  Analog Employees 
    on Feb 1, 2012 9:06 AM

    Hello Vijay,

    Apologies for the delayed response to your email, it somehow slipped through the net.

    Can you let us know if you are still experiencing issues with interfacing to the AD7690?

    Unfortunately we don't have code to share with you at this time, therefore the best approach to resolving your issue would be to work with your schematic and the timing that you are issuing to the device.

    Can you please send these - you can send them through pm if that is more convenient.

    I look forward to hearing from you and resolving any remaining concerns you have with this ADC.

    Thanks in advance,


    P.s. we have a short survey under way right now to understand requirements for our ADC design tools. Please visit URL below if you are interested to participate/feedback to this survey. Thanks in advance.


  • Hello Catherine,

         Thanks for your reply. We are still facing the count fluctuation problem  with AD7690.

    We are reading the data through the timer interrupt function. The timer interrupt will happen for every 50 micro seconds (For reading the 18 bit data it takes 1milli sec). Due to this we are getting 1000 samples/sec. But the problem was, the ADC counts are fluctuating around  150 counts. By doing the averaging, fluctuations reduced to 40 counts.

    How, we can reduce these fluctuations?

    Is the averaging method can able to stabilize these 150 counts fluctuations? If no, please give an alternative solution for this problem

    * We are using the 17 bit data only.

    * Load cell output is given to the instrumentation amplifier AD8221. The output of the instrumentation amplifier is given to AD7690. we identified that the input to the ADC (Vin+) was stable (no fluctuations at all). VIN- pin is grounded.

    * We are reading the data through falling edge.

    Thanks and Regards,


  • 0
    •  Analog Employees 
    on Apr 20, 2012 5:49 PM

    Hi Vijay,

    Sorry for the late reply. The AD7690 is a fully differential input. This means the positive and negative inputs must be antiphase around the common mode voltage Vref/2, the IN- pin cannot be tied to ground for proper operation. Is 18 bit performance important to you? If so you can use an amp such as the ADA4941 to perform singe ended to differential conversion.

    Best Rgds,