LM3S5C31 Datasheet, PDF (630/1220 Pages) Texas Instruments – Stellaris® LM3S5C31 Microcontroller

Analog-to-Digital Converter (ADC)
Figure 13-7. ADC Input Equivalency Diagram
VDD
ESD
Clamp
R_ADC
V_IN
ESD
Clamp
I_L
Stellaris® Microcontroller
12-bit
converter
C_ADC
Sample and hold
ADC converter
The ADC operates from both the 3.3-V analog and 1.2-V digital power supplies. The ADC clock can
be configured to reduce power consumption when ADC conversions are not required (see “System
Control” on page 198). The analog inputs are connected to the ADC through specially balanced input
paths to minimize the distortion and cross-talk on the inputs. Detailed information on the ADC power
supplies and analog inputs can be found in “Analog-to-Digital Converter (ADC)” on page 1162.
13.3.4.1
Internal Voltage Reference
The band-gap circuitry generates an internal 3.0 V reference that can be used by the ADC to produce
a conversion value from the selected analog input. The range of this conversion value is from 0x000
to 0xFFF in 12-bit mode, or 0x3FF in 10-bit mode. In single-ended-input mode, the 0x000 value
corresponds to an analog input voltage of 0.0 V; the 0xFFF in 12-bit mode, or 0x3FF in 10-bit mode
value corresponds to an analog input voltage of 3.0 V. This configuration results in a resolution of
approximately 0.7 mV in 12-bit mode and 2.9 mV per ADC code in 10-bit mode. While the analog
input pads can handle voltages beyond this range, the ADC conversions saturate in under-voltage
and over-voltage cases. Figure 13-8 on page 631 shows the ADC conversion function of the analog
inputs.
630
January 23, 2012
Texas Instruments-Production Data