Datasheet

 2009-2016 Microchip Technology Inc. DS40001365F-page 231
PIC18(L)F1XK22
20.0 FIXED VOLTAGE REFERENCE
(FVR)
The Fixed Voltage Reference, or FVR, is a stable
voltage reference, independent of V
DD, 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 FVR1EN bit of
the VREFCON0 register.
20.1 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 FVR1S<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, (FVR1BUF2) 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 16.0 “Analog-to-Digital Converter
(ADC) Module”, Section 21.0 “Digital-to-Analog
Converter (DAC) Module” and Section 17.0 “Com-
parator Module”.
20.2 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 FVR1ST bit of the VREFCON0 register will be set.
See Table 26-23 for the minimum delay requirement.
FIGURE 20-1: VOLTAGE REFERENCE BLOCK DIAGRAM
to Comparators, DAC
x1
x2
x4
+
-
FVR1EN
FVR1ST
2
FVR1S<1:0>
to ADC module
x1
x2
x4
FVR1BUF1
FVR1BUF2
1.024V
Fixed
Voltage
Reference
Note 1: FVR_buf2_enable = ‘1’ when (ADON = ‘1’)AND [(PVCFG<1:0> = ‘10’) OR ( CHS<4:0> = ‘11111’)]
FVR_buf2_enable
(1)