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Similar microcontroller to F2802x, but with 5V ADC?

LAURA SANDOVAL
Intellectual 360 points

I have run into some limitations with the range of the ADC pins on the C2000 F28027. 3.3V just isn't enough. I've done a lot of coding already. Any advice on a similar microcontroller, but with 5V ADC pins? Hopefully I won't have to start all over with the programming. Thanks!

  • 0
    TI__Guru 60865 points
    Hi Laura,

    If the voltages you want to sample are higher than 3.3V, use a resistive voltage divider or op-amp circuit with fractional gain to get the input signal into range.
  • 0 in reply to Devin Cottier
    Intellectual 360 points
    Hi Devin,

    Thank you so much for your response. Those are both great suggestions, however, the problem is with resolution of the signal that I want. My current set-up is a pressure sensor with a 39 mV range. The signal from the pressure sensor (from a blood pressure cuff) goes to an in-amp. Afterwards, the signal goes to the C2000 ADC pin (after going through a low-pass filter). I must filter the signal in the C code to measure small oscillations in the signal (see figure in website: www.sensorzine.com/.../digital-blood-pressure-meter-freescales-application-note-page3-724300.jpg). If the oscillations have not been amplified enough (>10 mV) then I run into noise issues.

    So, in short, the only thing that I can think of is a larger voltage range. I also would like the microcontroller to have the same memory as the C2000 F28027 (12 KB of RAM). Suggestions?
  • 0 in reply to LAURA SANDOVAL
    TI__Guru 60865 points
    If you scope the input to the ADC, does it look like figure 3 or figure 4? (Since they are using an 8-bit ADC in the application note, it seems like the raw ADC input would have to be similar to figure 4).
  • 0 in reply to Devin Cottier
    TI__Guru 60865 points
    You can also look at is the noise performance of the op-amp or instrumentation amp that you are using. This noise is usually specified as input referred, so gaining-up the signal more won't help (the same is also true if the noise you are seeing is introduced to the signal before the input of the amp).