PIC12F629/675
The following equations determine the output voltages:
6.5
Comparator Reference
VRR = 1 (low range): CVREF = (VR3:VR0 / 24) x VDD
The comparator module also allows the selection of an
internally generated voltage reference for one of the
comparator inputs. The internal reference signal is
used for four of the eight Comparator modes. The
VRCON register, Register 6-2, controls the voltage
reference module shown in Figure 6-5.
VRR = 0 (high range): CVREF = (VDD / 4) + (VR3:VR0 x
VDD / 32)
6.5.2
VOLTAGE REFERENCE
ACCURACY/ERROR
6.5.1
CONFIGURING THE VOLTAGE
REFERENCE
The full range of VSS to VDD cannot be realized due to
the construction of the module. The transistors on the
top and bottom of the resistor ladder network
(Figure 6-5) keep CVREF from approaching VSS or
VDD. The Voltage Reference is VDD derived and there-
fore, the CVREF output changes with fluctuations in
VDD. The tested absolute accuracy of the Comparator
Voltage Reference can be found in Section 12.0
“Electrical Specifications”.
The voltage reference can output 32 distinct voltage
levels, 16 in a high range and 16 in a low range.
FIGURE 6-5:
COMPARATOR VOLTAGE REFERENCE BLOCK DIAGRAM
16 Stages
8R
R
R
R
R
VDD
VRR
8R
16-1 Analog
MUX
VREN
CVREF to
Comparator
Input
VR3:VR0
While the comparator is enabled during Sleep, an inter-
rupt will wake-up the device. If the device wakes up
from Sleep, the contents of the CMCON and VRCON
registers are not affected.
6.6
Comparator Response Time
Response time is the minimum time, after selecting a
new reference voltage or input source, before the
comparator output is ensured to have a valid level. If
the internal reference is changed, the maximum delay
of the internal voltage reference must be considered
when using the comparator outputs. Otherwise, the
maximum delay of the comparators should be used
(Table 12-7).
6.8
Effects of a Reset
A device Reset forces the CMCON and VRCON
registers to their Reset states. This forces the
comparator module to be in the Comparator Reset
mode, CM2:CM0 = 000and the voltage reference to its
off state. Thus, all potential inputs are analog inputs
with the comparator and voltage reference disabled to
consume the smallest current possible.
6.7
Operation During Sleep
Both the comparator and voltage reference, if enabled
before entering Sleep mode, remain active during
Sleep. This results in higher Sleep currents than shown
in the power-down specifications. The additional cur-
rent consumed by the comparator and the voltage ref-
erence is shown separately in the specifications. To
minimize power consumption while in Sleep mode, turn
off the comparator, CM2:CM0 = 111, and voltage refer-
ence, VRCON<7> = 0.
2010 Microchip Technology Inc.
DS41190G-page 41
MICROCHIP [ MICROCHIP ]
