• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 234 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DDC112: Range Control Inputs

Clifford Greenblatt
Prodigy 90 points
Part Number: DDC112

The DDC112 has three range control inputs. From Figure 3 of the data sheet it appears that range selection is instantaneous and asynchronous. Is this true? Is there a point in time that the range controls can be changed without corrupting a sample? If not, what sample must be thrown out as invalid? Is there an ideal point in time to change the range control inputs?

  • 0
    TI__Genius 11550 points

    Hi Clifford,

    Welcome to the E2E forum. 

    The range selection is asynchronous and will change the integration capacitor based on the selection. Depending on where the range selection is changed, it is recommended to discard the data from the A-side and B-side to ensure all the subsequence integration data is correct. For normal case, the range selection should be changed before applying the CONV signal to the device.

    Thanks.

    -TC

  • 0 in reply to TCT
    Prodigy 90 points

    Your response is definitely helpful, although I am disappointed that the device was not designed to change range synchronously. It would have been ideal if the range for each side were clocked in immediately after measurement is completed for that side. That way, no samples would need to be discarded. However, I need to work with the real device and accept the need to discard samples. 

    Could there be a way to salvage one of the samples? Suppose the range is changed at the moment data first becomes valid for side A. I know this will wreck integration still in progress for side B, but I am confident that the measurement for side A will be good. This, however leaves a question about the Side A integration that follows. I think that changing the range during the reset or autozero part of the cycle might wreck the next integration for side A, but could there be a little bit of time from the moment side A data becomes valid to make the range change before reset and autozero begin? 

  • 0 in reply to Clifford Greenblatt
    TI__Genius 11550 points

    Hi Clifford,

    You are correct in the description of how changing the range will affect the A-side and the B-side data. If you change the range selection in the WAIT phase after the CONVERT phase and before the RESET phase then you will only need to discard the data in the side that is integrating. I don't have the exact timing for when the RESET phase occurs after the CONVERT phase. This time also changes depending on how long is the integration time. I hope this helps with the design of your system.

    Thanks.

    -TC 

  • 0 in reply to TCT
    Prodigy 90 points

    Thank you for validating my conjecture about how a sample may avoid being corrupted by a range change. I can make the range change almost immediately after data becomes valid, so I think that would be a safe way to protect the integration that follows. I consider the issue resolved.