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new issue about ADS1211

James Hao63957
Prodigy 120 points

Other Parts Discussed in Thread: ADS1211

4152.schema.zip

Hi All,

I am doing a data acquire project with ads1211, and I use Vbias to extend measure range, however, sometimes when I turn on the power, and send the instruction (char '7') to ads1211 with no load (End5 and End4 open), I can read the output as (32 3A 39 33 35 37, convert to hex is: 2A 93 57 in offset binary) instead of a value very close to zero, I measure the Vbias as normal (around 3.3V), but I measure the voltage between A1n1N and A1n1P is around 3.3V, this is why? is the expected voltage around zero?

But sometimes I can read a very smalll output as expected, I don't know why? could you please have a look for me, thanks.

Attachment is my code and circuit schem.2133.BETLIB.zip

Regards!

James

 

  • 0
    TI__Guru** 113765 points

    James,

    I notice from your schematic that you have no load caps on the crystal and no bypass caps on the supply pins of the ADS1211. 

    Are you sure that the crystal has started to oscillate in the situations where you get the unexpected readings? It appears to me that your system may be unstable.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 120 points

    Hi Bob, Thank you for your quick response, in the schem sheet, I missed one load capacitor on supply pin of the ADS1211, and the capacitor is on the circuit board, according to your suggest, I need to add load capacitors to two crystals to make them more stable.

    I made two circuit boards with the same schema design, after I choose the other board, it works fine almost every time, and I measure the voltage diff between A1n1N and A1n1P, it is almost 0.01 mV, pretty stable.

    I want to know whether there is some apparent cause (both hardware and software) to make the input voltage diff is so big?

    Best Regards!

    James

     

  • 0 in reply to James Hao63957
    TI__Guru** 113765 points

    James,

    If you measure with a meter that you have 3.3V between AIN1N and AIN1P for the circuit your provided, then I would look for a short between AIN1N and AGND as the pins are next to one another. 

    Another possibility is that the ADS1211 has been damaged.  The bottom line is that one of the inputs is being pulled to ground if you see a difference of 3.3V with a volt meter measuring across the input pins.

    Best regards,

    Bob B

  • 0
    Prodigy 40 points

     

    Is there    any    ads1211  timing diagram scenario longer than in  datasheet  for example            

                                                    STEPS RESPECTIVELY:

      1.)send instruction cmd

                     2.)send bytes or reads  bytes      "  there are only two step in  timing diagram ads1211 datasheet         

                                                                            |                                        diagram other steps ignored at  datasheet timing diagram."

                                                                            |

                                                      3.)again send instruction cmd

             4.)again  send bytes or reads bytes

                                                     5.)again send instruction cmd

             6.)again  send bytes or reads bytes

                                                                      ....... ..!!