12F615 datasheet(62/168 Pages) MICROCHIP

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PIC12F609/615/12HV609/615

DS41302A-page 60

Preliminary

8.10

Comparator Voltage Reference

The Comparator Voltage Reference module provides

an internally generated voltage reference for the com-

parators. The following features are available:

• Independent from Comparator operation

• 16-level voltage range

• Output clamped to VSS

• Ratiometric with VDD

• Fixed Reference (0.6)

The VRCON register (Register 8-3) controls the Volt-

age Reference module shown in Register 8-6.

8.10.1

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.

8.10.2

OUTPUT VOLTAGE SELECTION

The

CVREF voltage reference has 2 ranges with 16

voltage levels in each range. Range selection is con-

trolled by the VRR bit of the VRCON register. The 16

levels are set with the VR<3:0> bits of the VRCON reg-

ister.

The CVREF output voltage is determined by the

following equations:

EQUATION 8-1:

CVREF OUTPUT VOLTAGE

The full range of VSS to VDD cannot be realized due to

the construction of the module. See Figure 8-6.

8.10.3

OUTPUT CLAMPED TO VSS

The CVREF output voltage can be set to Vss with no

power consumption by configuring VRCON as follows:

•VREN = 0

•VRR = 1

•VR<3:0> = 0000

This allows the comparator to detect a zero-crossing

while not consuming additional CVREF module current.

8.10.4

OUTPUT RATIOMETRIC TO VDD

The comparator voltage reference is VDD derived and

therefore, the CVREF output changes with fluctuations in

VDD. The tested absolute accuracy of the Comparator

Voltage Reference can be found in Section 15.0

“Electrical Specifications”.

8.10.5

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

the HFINTOSC oscillator is active.

8.10.6

FIXED VOLTAGE REFERENCE

STABILIZATION PERIOD

When the Fixed Voltage Reference module is enabled,

it will require some time for the reference and its ampli-

fier circuits to stabilize. The user program must include

a small delay routine to allow the module to settle. See

Section 15.0 “Electrical Specifications” for the

minimum delay requirement.

8.10.7

VOLTAGE REFERENCE

SELECTION

Multiplexers on the output of the Voltage Reference

module enable selection of either the CVREF or fixed

voltage reference for use by the comparators.

Setting the CMVREN bit of the VRCON register

enables current to flow in the CVREF voltage divider

and selects the CVREF 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

CVREF voltage divider is disabled minimizing the power

drain of the voltage reference peripheral.

VRR

1 (low range):

VRR

0 (high range):

CVREF

(VDD/4) +

CVREF

(VR<3:0>/24)

VDD

(VR<3:0>

VDD/32)

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