LM3S3749 Luminary Micro, Inc, LM3S3749 Datasheet - Page 358

• Manufacturer Part Number: LM3S3749
• Description: Lm3s3749 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Analog-to-Digital Converter (ADC)
358
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 13-2 on page 358 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 13-3 on page 358 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
13-4 on page 359 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 13-2. Differential Sampling Range, V
Figure 13-3. Differential Sampling Range, V
-1.5 V
-1.5 V
0 V
-0.75 V
0 V
ADC Conversion Result
0x3FF
0x1FF
ADC Conversion Result
0x3FF
0x1FF
+0.75 V
- Input Saturation
V
IN_ODD
- Input Saturation
1.5 V
0x0FF
0 V
= 1.5 V
Preliminary
IN_ODD
IN_ODD
+2.25 V
= 1.5 V
= 0.75 V
+1.5 V
3.0 V
1.5 V
V
V
IN_EVEN
V
V
IN_EVEN
June 02, 2008