ADUC834: Why is there a different result when using internal voltage ref compared to external 2.5V ref?

Document created by analog-archivist Employee on Feb 23, 2016
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The ADC result when using the internal reference is totally different than when
using a 2.5V
external reference. Why?

 

The internal reference for the ADCs is 1.25V and not 2.5V (as with the
ADuC812). This means
that when converting on the particular voltage ranges as selected by ADC0CON
that the ranges are
actually half of those specified (they are specified assuming a 2.5V
reference). The internal
reference is not recommended for high accuracy ADC conversion. Instead a
voltage reference such
as the AD780 is recommended. Although the internal reference for the ADC is
only 1.25V the
internal reference for the DAC is still 2.5V

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