• Locked Locked
  • Replies 6 replies
  • Subscribers 45 subscribers
  • Views 532 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.

ADS1212 Cannot Write Bit Zero of CMR Byte 1--Always Zero.

Chris Harthan
Prodigy 180 points

This has been an ongoing issue. Replacing the chip fixes the problem.

Here is a scope trace of the register write measured at the ADS1212 pins...

When I read it back, the bit is zero....

(I have a long ground lead on my scope probe. It's not as noisy as these traces would suggest.)

This is not intermittent. This part does it every time. I checked the DRDY line and the A/D data rate matches the register settings I read back. Unfortunately, it's the wrong rate.  It appears that on some chips, bit zero of byte one (DR8) cannot be changed from it's default value of zero.

I have a 2MHz clock rate.

I can hang onto this board for a couple of weeks if there is something you would like me to try.

Thanks,

Chris


  • TI__Guru** 112765 points

    Hi Chris,

    This sounds like it might be a stuck bit in the register.  You say that this is an ongoing problem.  Can you be more specific as to the number of occurrences that you have seen?  Are these new units (as opposed to customer returns)?  Also, do you see that the same register bit is having this issue or is it different bits/registers that you see this problem?  Do the problem units appear to be from the same lot (same lot trace codes on the top of the devices)?

    Thanks,

    Bob B

  • in reply to Bob Benjamin
    Prodigy 180 points
    Hi Bob,
    Thanks for the reply. These are new units. Our production supervisor is going to get me more information about how many parts we replaced in the last few months. I will follow up.

    The code on the part I have is 49W9N1B.

    Our data rates only span a portion of the available decimation ratios, so I don't know conclusively if it is only the one bit. I am going to write a debug script that should answer that question. I will let you know what I find.

    Thanks,
    Chris
  • in reply to Bob Benjamin
    Prodigy 180 points
    Hi Bob,
    I have more information about the data rate portion of the CMR. Some CMR bits can't be changed without my losing communication with the chip. It does appear to only be bit 0 that has a problem.

    Here I write a 1F FF to the DR portion of the CMR...

    Wrote word data 0042 to address 4204
    Wrote word data 001f to address 4203
    Wrote word data 00ff to address 4202
    Wrote word data 006b to address 4201

    Here I read it back...

    Read 0042 from address 4204
    Read 001f from address 4203
    Read 00fe from address 4202
    Read 006b from address 4201

    These are just debug commands that let me talk directly to my hardware.
    You can see that it read back 1F FE.

    Chris
  • in reply to Bob Benjamin
    Prodigy 180 points

    Hi Bob,

    Our production manager gave me some numbers.

    This year we purchased 4,590 parts. He documented failures of 70 parts. It's possible that some of these had different failures. He did not have a complete record.

    I was given a bag of 12 rejected parts and they had the following codes...

    QTY: 2   48W43KB

    QTY: 6   49W49LB

    QTY: 1   46WFR3B

    QTY3:   46WKL5B

    Chris

  • in reply to Chris Harthan
    TI__Guru** 112765 points

    Hi Chris,

    Thanks for the info.  I will have to do a little research and get back to you as soon as I can, which will most likely be next week due to the holidays.

    Best regards,

    Bob B

  • in reply to Bob Benjamin
    TI__Guru** 112765 points

    Hi Chris,

    I had someone from our quality team check on this and as of today there have been no other failure reports or submissions with respect to the lot trace codes you have given.  It would be best if you can submit the devices back to TI for further analysis.  Information regarding customer returns can be found at:

    If you purchased the devices through a distributer it would be best to contact them to initiate the processing.

    Best regards,

    Bob B