Important: The ASRCP bits in the ACCTL register must be set before using the analog comparators.
22.3.1 Internal Reference Programming
The structure of the internal reference is shown in Figure 22-3 on page 1656. The internal reference
is controlled by a single configuration register (ACREFCTL).
Figure 22-3. Comparator Internal Reference Structure
N*R
N*R
0x00x10xE0xF
Decoder
internal
reference
V
IREF
Note: In the figure above, N*R represents a multiple of the R value that produces the results specified
in Table 22-2 on page 1656.
The internal reference can be programmed in one of two modes (low range or high range) depending
on the RNG bit in the ACREFCTL register. When RNG is clear, the internal reference is in high-range
mode, and when RNG is set the internal reference is in low-range mode.
In each range, the internal reference, V
IREF
, has 16 preprogrammed thresholds or step values. The
threshold to be used to compare the external input voltage against is selected using the VREF field
in the ACREFCTL register.
In the high-range mode, the V
IREF
threshold voltages start at the ideal high-range starting voltage
of V
DDA
/4.2 and increase in ideal constant voltage steps of V
DDA
/29.4.
In the low-range mode, the V
IREF
threshold voltages start at 0 V and increase in ideal constant
voltage steps of V
DDA
/22.12. The ideal V
IREF
step voltages for each mode and their dependence
on the RNG and VREF fields are summarized in Table 22-2.
Table 22-2. Internal Reference Voltage and ACREFCTL Field Values
Output Reference Voltage Based on VREF Field Value
ACREFCTL Register
RNG Bit ValueEN Bit Value
0 V (GND) for any value of VREF. It is recommended that RNG=1 and VREF=0 to
minimize noise on the reference ground.
RNG=XEN=0
June 18, 20141656
Texas Instruments-Production Data
Analog Comparators
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