LM3S6952 Datasheet, PDF (286/626 Pages) Texas Instruments – Stellaris LM3S6952 Microcontroller

Analog-to-Digital Converter (ADC)
■ If ∆V < 0, then the conversion result < 0x1FF (range is 0–0x1FF)
The differential pairs assign polarities to the analog inputs: the even-numbered input is always
positive, and the odd-numbered input is always negative. In order for a valid conversion result to
appear, the negative input must be in the range of ± 1.5 V of the positive input. If an analog input
is greater than 3 V or less than 0 V (the valid range for analog inputs), the input voltage is clipped,
meaning it appears as either 3 V or 0 V, respectively, to the ADC.
Figure 12-2 on page 286 shows an example of the negative input centered at 1.5 V. In this
configuration, the differential range spans from -1.5 V to 1.5 V. Figure 12-3 on page 287 shows an
example where the negative input is centered at -0.75 V, meaning inputs on the positive input
saturate past a differential voltage of -0.75 V since the input voltage is less than 0 V. Figure
12-4 on page 287 shows an example of the negative input centered at 2.25 V, where inputs on the
positive channel saturate past a differential voltage of 0.75 V since the input voltage would be greater
than 3 V.
Figure 12-2. Differential Sampling Range, V_{IN_ODD} = 1.5 V
ADC Conversion Result
0x3FF
0x1FF
0V
-1.5 V
1.5 V
0V
V_{IN_ODD} = 1.5 V
- Input Saturation
3.0 V V_{IN_EVEN}
1.5 V DV
286
April 05, 2010
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