PIC16F631 datasheet(107/294 Pages) MICROCHIP

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DS41262D-page 105

PIC16F631/677/685/687/689/690

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 VP6EN 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

amplifier circuits to stabilize. The user program must

include a small delay routine to allow the module to

settle. See the electrical specifications section 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 C1VREN bit of the VRCON register enables

current to flow in the CVREF voltage divider and selects

the CVREF voltage for use by C1. Clearing the C1VREN

bit selects the fixed voltage for use by C1.

Setting the C2VREN bit of the VRCON register enables

current to flow in the CVREF voltage divider and selects

the CVREF voltage for use by C2. Clearing the C2VREN

bit selects the fixed voltage for use by C2.

When both the C1VREN and C2VREN bits are cleared,

current flow in the CVREF voltage divider is disabled

minimizing the power drain of the voltage reference

peripheral.

FIGURE 8-8:

COMPARATOR VOLTAGE REFERENCE BLOCK DIAGRAM

VRR

VR<3:0>(1)

16-1 Analog

16 Stages

VDD

MUX

Fixed Voltage

C2VREN

C1VREN

CVREF

Reference

VP6EN

Sleep

HFINTOSC enable

0.6V

FixedRef

To Comparators

and ADC module

To Comparators

and ADC module

Note 1:

Care should be taken to ensure VREF remains

within the comparator common mode input

range. See Section 17.0 “Electrical Specifica-

tions” for more detail.

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