Datasheet

PIC12F609/615/617/12HV609/615
DS41302D-page 74  2010 Microchip Technology Inc.
9.10 Comparator Voltage Reference
The Comparator Voltage Reference module provides
an internally generated voltage reference for the
comparators. The following features are available:
• Independent from Comparator operation
• 16-level voltage range
• Output clamped to V
SS
• Ratiometric with VDD
• Fixed Reference (0.6)
The VRCON register (Register 9-3) controls the
Voltage Reference module shown in Register 9-6.
9.10.1 INDEPENDENT OPERATION
The comparator voltage reference is independent of
the comparator configuration. Setting the VREN bit of
the VRCON register will enable the voltage reference.
9.10.2 OUTPUT VOLTAGE SELECTION
The CVREF voltage reference has 2 ranges with 16
voltage levels in each range. Range selection is
controlled by the VRR bit of the VRCON register. The
16 levels are set with the VR<3:0> bits of the VRCON
register.
The CVREF output voltage is determined by the
following equations:
EQUATION 9-1: CVREF OUTPUT VOLTAGE
The full range of VSS to VDD cannot be realized due to
the construction of the module. See Figure 9-6.
9.10.3 OUTPUT CLAMPED TO VSS
The CVREF output voltage can be set to Vss with no
power consumption by configuring VRCON as follows:
• FVREN = 0
This allows the comparator to detect a zero-crossing
while not consuming additional CV
REF module current.
9.10.4 OUTPUT RATIOMETRIC TO VDD
The comparator voltage reference is VDD derived and
therefore, the CV
REF output changes with fluctuations in
V
DD. The tested absolute accuracy of the Comparator
Voltage Reference can be found in Section 16.0
“Electrical Specifications”.
9.10.5 FIXED VOLTAGE REFERENCE
The fixed voltage reference is independent of VDD, with
a nominal output voltage of 0.6V. This reference can be
enabled by setting the FVREN bit of the VRCON
register to ‘1’. This reference is always enabled when
the HFINTOSC oscillator is active.
9.10.6 FIXED VOLTAGE REFERENCE
STABILIZATION PERIOD
When the Fixed Voltage Reference module is enabled,
it will require some time for the reference and its
amplifier circuits to stabilize. The user program must
include a small delay routine to allow the module to
settle. See Section 16.0 “Electrical Specifications”
for the minimum delay requirement.
9.10.7 VOLTAGE REFERENCE
SELECTION
Multiplexers on the output of the Voltage Reference
module enable selection of either the CV
REF or fixed
voltage reference for use by the comparators.
Setting the CMVREN bit of the VRCON register
enables current to flow in the CV
REF voltage divider
and selects the CV
REF voltage for use by the Compar-
ator. Clearing the CMVREN bit selects the fixed voltage
for use by the Comparator.
When the CMVREN bit is cleared, current flow in the
CV
REF voltage divider is disabled minimizing the power
drain of the voltage reference peripheral.
VRR 1 (low range):=
VRR 0 (high range):=
CV
REF (VDD/4) + =
CV
REF (VR<3:0>/24) VDD=
(VR<3:0> V
DD/32)