AD7859 Full Self-Calibration

I am having an issue getting the AD7859 to consistently perform a full self-calibration.

AVDD and DVDD are at 5V with a stable external 5V reference.

My clock is running at about 3.75MHz.

I do not see any activity on the CS.

About 1 out of every 25 times, when I pull the /CAL pin low for 10us and then release it back to 5V I do not see the BUSY line go high.

Because of this when my software goes to perform its first conversion, the chip does a calibration and my conversion fails.

Is there any documentation of using the /CAL pin to perform the full self-calibration as the datasheet only full explains using the /CONVST pin?

What are the potential reasons the full self-calibration did not start when the /CAL pin was taken from low to high?

  • 0
    •  Analog Employees 
    on Apr 21, 2014 9:43 PM

    Hi Mike,

    Please try the timing diagram below for the AD7859 self-calibration using /CAL pin.

    Regards,

    Jonathan

  • Jonathan,

    Thank you.  I have tried adjusting my /CAL pulse from 200ns up to around 10us.  When it works, t15 is 2.5tclkin or less (usually I see 2tclkin).  My problem is that sometime BUSY does not come high.  I have not been able to find a reason why it does not always start the calibration.  The external reference is stable and looks the same for a passed case.  And the clock has good edges, same frequency and duty cycle for both cases.  The only other reason Analog Devices has been able to give is if the Test Register is somehow corrupted and suggested writing 0000_0000_0000_0010 to reset the parallel interface, and that is also in their datasheet on page 25 and you mentioned it earlier too.  So far, nothing has fixed my issue.

    Thanks,

    Mike

  • 0
    •  Analog Employees 
    on Jun 27, 2014 12:45 AM


    Hi Mike,

         Have you discuss this issue with the CIC america? They have a discussion on this problem. I thought that you were in the same group that had a communication with the CIC.

    Regards,

    Jonathan