PIC18F23K22-ESLASHML datasheet(337/496 Pages) MICROCHIP

337 / 496 page

 2010 Microchip Technology Inc.

Preliminary

DS41412C-page 337

PIC18(L)F2X/4XK22

21.0 FIXED VOLTAGE REFERENCE

(FVR)

The Fixed Voltage Reference, or FVR, is a stable

voltage reference, independent of VDD, with 1.024V,

2.048V or 4.096V selectable output levels. The output

of the FVR can be configured to supply a reference

voltage to the following:

• ADC input channel

• ADC positive reference

• Comparator positive input

• Digital-to-Analog Converter (DAC)

The FVR can be enabled by setting the FVREN bit of

the VREFCON0 register.

21.1

Independent Gain Amplifiers

The output of the FVR supplied to the ADC,

Comparators and DAC is routed through an

independent

programmable gain

amplifier.

The

amplifier can be configured to amplify the 1.024V

reference voltage by 1x, 2x or 4x, to produce the three

possible voltage levels.

The FVRS<1:0> bits of the VREFCON0 register are

used to enable and configure the gain amplifier settings

for the reference supplied to the DAC and Comparator

modules. When the ADC module is configured to use

the FVR output, (FVR BUF2) the reference is buffered

through an additional unity gain amplifier. This buffer is

disabled if the ADC is not configured to use the FVR.

For specific use of the FVR, refer to the specific module

sections: Section 17.0 “Analog-to-Digital Converter

(ADC) Module”, Section 22.0 “Digital-to-Analog

Converter (DAC) Module” and Section 18.0 “Com-

parator Module”.

21.2

FVR Stabilization Period

When the Fixed Voltage Reference module is enabled, it

requires time for the reference and amplifier circuits to

stabilize. Once the circuits stabilize and are ready for use,

the FVRST bit of the VREFCON0 register will be set. See

Section 27.0 “Electrical Characteristics” for the

minimum delay requirement.

FIGURE 21-1:

VOLTAGE REFERENCE BLOCK DIAGRAM

FVRS<1:0>

FVR BUF2

(To ADC Module)

FVR BUF1

(To Comparators, DAC)

FVREN

FVRST

1.024V Fixed

Reference

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