Texas Instruments MSP430x4xx Family, User Manual

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Comparator_A Operation
23-5 Comparator_A
23.2.3 Output Filter
The output of the comparator can be used with or without internal filtering.
When control bit CAF is set, the output is filtered with an on-chip RC-filter.
Any comparator output oscillates if the voltage difference across the input
terminals is small. Internal and external parasitic effects and cross coupling on
and between signal lines, power supply lines, and other parts of the system
are responsible for this behavior as shown in Figure 23−2. The comparator
output oscillation reduces accuracy and resolution of the comparison result.
Selecting the output filter can reduce errors associated with comparator
oscillation.
Figure 23−2. RC-Filter Response at the Output of the Comparator
+ Terminal
− Terminal
Comparator Inputs
Comparator Output
Unfiltered at CAOUT
Comparator Output
Filtered at CAOUT
23.2.4 Voltage Reference Generator
The voltage reference generator is used to generate V
CAREF
, which can be
applied to either comparator input terminal. The CAREFx bits control the
output of the voltage generator. The CARSEL bit selects the comparator
terminal to which V
CAREF
is applied. If external signals are applied to both
comparator input terminals, the internal reference generator should be turned
off to reduce current consumption. The voltage reference generator can
generate a fraction of the device’s V
CC
or a fixed transistor threshold voltage
of ~ 0.55 V.