Table 22-2. Internal Reference Voltage and ACREFCTL Field Values (continued)
Output Reference Voltage Based on VREF Field Value
ACREFCTL Register
RNG
Bit Value
EN
Bit Value
V
IREF
High Range: 16 voltage threshold values indexed by
VREF
= 0x0 .. 0xF
Ideal starting voltage (
VREF
=0): V
DDA
/ 4.2
Ideal step size: V
DDA
/ 29.4
Ideal V
IREF
threshold values: V
IREF
(
VREF
) = V
DDA
/ 4.2 +
VREF
* (V
DDA
/ 29.4), for
VREF
= 0x0 .. 0xF
For minimum and maximum V
IREF
threshold values, see Table 22-3 on page 1657.
RNG
=0
EN
=1
V
IREF
Low Range: 16 voltage threshold values indexed by
VREF
= 0x0 .. 0xF
Ideal starting voltage (
VREF
=0): 0 V
Ideal step size: V
DDA
/ 22.12
Ideal V
IREF
threshold values: V
IREF
(
VREF
) =
VREF
* (V
DDA
/ 22.12), for
VREF
= 0x0 ..
0xF
For minimum and maximum V
IREF
threshold values, see Table 22-4 on page 1658.
RNG
=1
Note that the values shown in Table 22-2 are the ideal values of the V
IREF
thresholds. These values
actually vary between minimum and maximum values for each threshold step, depending on process
and temperature. The minimum and maximum values for each step are given by:
■ V
IREF
(
VREF
) [Min] = Ideal V
IREF
(
VREF
) – (Ideal Step size – 2 mV) / 2
■ V
IREF
(
VREF
) [Max] = Ideal V
IREF
(
VREF
) + (Ideal Step size – 2 mV) / 2
Examples of minimum and maximum V
IREF
values for V
DDA
= 3.3V for high and low ranges, are
shown inTable 22-3 and Table 22-4. Note that these examples are only valid for V
DDA
= 3.3V; values
scale up and down with V
DDA
.
Table 22-3. Analog Comparator Voltage Reference Characteristics, V
DDA
= 3.3V, EN= 1, and
RNG = 0
Unit
V
IREF
Max
Ideal V
IREF
V
IREF
Min
VREF
Value
V
0.841
0.786
0.731
0x0
V
0.953
0.898
0.843
0x1
V
1.065
1.010
0.955
0x2
V
1.178
1.122
1.067
0x3
V
1.290
1.235
1.180
0x4
V
1.402
1.347
1.292
0x5
V
1.514
1.459
1.404
0x6
V
1.627
1.571
1.516
0x7
V
1.739
1.684
1.629
0x8
V
1.851
1.796
1.741
0x9
V
1.963
1.908
1.853
0xA
V
2.076
2.020
1.965
0xB
V
2.188
2.133
2.078
0xC
V
2.300
2.245
2.190
0xD
V
2.412
2.357
2.302
0xE
V
2.525
2.469
2.414
0xF
1657
June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller