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MSP430 ADC

Simon Attard
Intellectual 775 points

Hi all,

I am using a development kit which uses the MSP430 as its processor. I would like to know something about the ADC.

I am using the 12-bit ADC with internal voltage reference. How will the ADC readings change, when the battery begins to discharge, and its voltage gets lower? Will the maximum input voltage of the ADC remain the same?

I know these are basic questions, but could not find info on the data sheet. Any links to the required data will be much appreciated.

Thanks a lot.

  • 0
    Guru 12160 points

    In the data sheet for your specific flavor of MSP430, you'll find an "Absolute Maximum Ratings" section.  It tells you the minimum and maximum voltages you can apply to any pin.  The spec is usually GND-0.3V to Vcc+0.3V.

    So if your hardware design allows Vcc to fall as the battery voltage falls, then you may need to take special care to avoid applying voltages higher than Vcc+0.3V to an ADC input pin.

    As for the readings you get from the ADC12, anything below the "-" reference you choose gives a zero reading.  Anything above the "+" reference you choose gives you a 4095 reading (or 1023 or 255 in reduced resolution modes).

    Your internal reference also requires a bit of voltage headroom on its supply side.  This too is in the data sheet, usually as "AVcc(min)".  If your hardware design allows AVcc to fall below AVcc(min) as the battery voltage falls, then your readings will be against a lower "+" reference than you intended, and the readings will suffer.

    If you have trouble finding the specs I mentioned, please let us know which MSP430 you are using or plan to use.

    Jeff

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