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ADS7953: MXO does not report same CH value

Andrea Guitta
Intellectual 290 points
Part Number: ADS7953


Tool/software:

Dear Sir

we are facing the following problem: MXO pin is never equal to the selected Ch.

Given that in idle condition we see MXO at 3.3V

When i want to read the ADC, for instance CH4 (forced externally to GND), the MXO moves from 3.3V to the expected CH value, but pin MXO do not show 0V, but an offset of about 0.5V.

See below: Yellow is the MXO pin and red is the SDI pin

See below the schematic

4846.ADS7953_sch.pdf

Notice that we have same result also bypassing the opamp between MXO and AINP (i.e.: mounting R118)

Notice also that if we separate MXO from AINP (AINP floating), however the issue is present on MXO, never equal to the selected channel...

We also tried other channels: CH1 is expected to be a steady 1.2V (measured with multimeter) Instead MXO reports almost 3.3V

Any clue on what's happening?

Andrea

  • 0
    TI__Mastermind 18220 points

    Hi Andrea,

    Thanks for providing the schematic. 

    Can you provide more information on when the device is programmed to select another channel, and when the voltage on the MXO pin is measured in relation to this? Have you tried this across multiple ADS7953 devices, and do they give a similar result?

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Intellectual 290 points

    Hello Joel

    i think we discovered the issue - some of the channels was receiving by mistake a 4V input (Vref set at 2,5V), and somehow this broke all other channels.

    Restoring all 16 Vin with a voltage <2.5V was succesfull, and now we are able to correctly read the digital value of the analog signal; and MXO behaves accordingly

    Best regards

    Andrea