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MSP430FR4131: ADC Conversion

Daviel Almonte
Expert 3055 points
Part Number: MSP430FR4131

The application manual states the formula for the ADC conversion as :

N=1024 (Vin-Vr-)/(Vr+ - Vr-)

Is there a minimum value for the  Vr+  -  Vr-  difference that is required for a reliable ADC operation. E.g. will the ADC produce accurate results if the difference between the positive and the negative reference voltages is , say,  0.5V

  • 0
    TI__Genius 12615 points

    Hi Daviel,

    I don't see any specification on the difference between these two. There is typically an absolute max or min value given for VR+ and VR-.  For microcontrollers with a 1.5V internal VREF, the minimum external VR+ is usually around 1.4V with a minimum VR- of around -0.2V.

    Hope this helps.

    BR,
    Leo

  • 0 in reply to Leonardo Estevez
    TI__Expert 3055 points

    but are there any limitation for the resulting (Vr+ - Vr- ) value? Such that if I set Vr+ = 2.0V, and Vr- = 1.9V, the  (Vr+ - Vr- ) = 100mV.  That set the resolution to  100mV/1024 = 97.6uV. 

    Will that be true for the ADC input voltage between 1.9V and 2.0V?

  • 0 in reply to Daviel Almonte
    Guru 96315 points

    I don't see that spec in the FR4133 data sheet. For the F5529, the minimum "differential external reference" is 1.4V. [Ref F5529 data sheet (SLAS590P) Sec 8.40]. That's a different chip, but maybe provides an order of magnitude.

  • 0 in reply to Bruce McKenney
    TI__Expert 3055 points

    Can a difference of 1.2V will work since this this spec isn't in the Data sheet? 

  • 0 in reply to Daviel Almonte
    Guru 96315 points

    I need to defer to the TI folk on this one. I'm not even quite sure what the symptom would be, maybe some non-linearity out at the edges of the range?

    I suppose you could just try it.

  • 0 in reply to Leonardo Estevez
    TI__Genius 11886 points

    Hi Leo,

    I see the FR5739 also has a 10-bit SAR ADC, and is an FRAM device, so can we use that as a guide here?  Is it the same ADC in FR413x?  (Similar thinking to Bruce's comment below).  

    The FR5739 spec's the Veref difference at 1.4V Minimum.  See datasheet section 5.32.

    Thanks,
    Darren

  • 0 in reply to Darren Jenkins
    TI__Genius 12615 points

    Hi Darren,

    Please excuse the delay as I was out of office. I believe it's reasonable to make this assumption for evaluation - although since this isn't clearly specified for FR4131, there's no guarantee that this will always work.

    BR,
    Leo

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