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ADS7828: read channel data

Amy Luo
Expert 6895 points

Part Number: ADS7828

Hi team,

When reading channel data, there will be occasional errors, and it will not be recovered after the error. You need to restart the chip.

The wiring is as shown in the above figure. Use internal 2.5V reference voltage, work in STAND mode, POWER DOWN mode 3, that is, PD1 = 1, PD0 = 0. The read time interval between channels is 500us.

A total of 100 sets of equipment, in the process of using, occasionally one of them will have a reading error every day. Under normal conditions, the readings of ADIN1 and ADIN2 are 1703, the readings of ADIN3 and ADIN4 are 0. When abnormal, the readings of ADIN1 and ADIN2 become 581, and the readings of ADIN3 and ADIN4 become 340. When abnormal, the voltage of ADIN1 and ADIN2 is normal 1.04v, the voltage of ADIN3 and ADIN4 is normal 0V, REF voltage is 2.5V, VCC_3.3V=3.3V.

After the error, changes the input voltage of the channel, its output is changed, but the amount of change is smaller.

When it is abnormal, the last three channels of ADS7828E are grounded. Theoretically, the read data should be 0, but the actual number read is more than 200, which is not normal.

In addition, channel 5 GM + in the circuit is also connected to the outside, which is in the suspended state. Is there a problem? Because when abnormal occurs, the voltage at GM + changes to 1.6 or 0.84v, which is not the normal 2.5V. Is the abnormal reading caused by the problem of this pin?

Best Regards,
Amy Luo

  • 0
    TI__Mastermind 25070 points

    Hello,

    This is interesting behavior. 

    My first thought, seeing how all channels are being affected by it, is that not one single channel can be the source of this. If layout between the channels and connections are all clean, then one channel cannot cause this.

    I would first look at the reference and at the power supplies. Make sure that there is no brown outs, or unexpected dips on any of those voltage rails. Even if the power rail is not going to zero, a large enough dip could cause issues. These rails would be able to affect all the channels. 

    Could you further describe what happens after the error? you mentioned that the reading does not go back, meaning it will continue to output the incorrect code? But when you change the input voltage, you mentioned that the output code does reflect a change? in what way? do all channels show the same response?

    Regards

    Cynthia