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SM320F28335-EP: ADC converter not working

Fred Stone
Prodigy 50 points
Part Number: SM320F28335-EP

we have 4 designs with basically the identical schematics.  3 are working fine but the ADC in the 4th one returns a 0 or 2041 steady value.  We are using the same code on all 4 designs.  All connection have been verified and the chips on a working and the non-working design are from the same purchased tray.

The only clue is that the ADCREFM voltage on the non-working design is higher (~1.5V) than the ADCREFP (~1.2V). while the ADCREFM oon the working designs is around (~0.8V).

  • 0
    TI__Guru 74070 points

    Fred,

    As you have mentioned ADCREFM = 1.5V should not be happening. Any issue with the ADCREFP/M voltages indicates that there is an issue with the ADC internal reference and you will have non-ideal ADC conversions as such.

    When you mention 4 designs with equivalent schematics, have you been able to change out the F28335 that is exhibiting this behavior with a new(or even a F28335 from one of the other 3 PCBs) to see if this still happens?

    From the above it sound like this one unit is an outlier, but would like to confirm this is true.  If possible to just swap this one device with one of the other 3 and see if the failure follows the device or board would be a indicator of where the issue lies.

    In terms of PCB connections, the only thing that could influence the voltage you see on the ADCREFP/M pins is the voltage on VDDA2/VDDAIO or the resistor on RESEXT(22kOhm).  Even then, I'm not sure we would see ADCREFP be in spec and ADCREFM be out of spec, but you can confirm that these connections look normal in addition to the above.

    I'll wait for your response and then we can go from their in terms of debug.

    Best,

    Matthew

  • 0 in reply to MatthewPate
    Prodigy 50 points

    Matt, I sent you an e-mail.  We have 5 boards that behave the same and voltage, curremt draw etc. are confirmed.  Can we have a 5 min phone call?

  • 0 in reply to Fred Stone
    TI__Guru 74070 points

    Email sent your way as well.

    Best,

    Matthew