Microchip Technology MA160014 Data Sheet

 2010-2012 Microchip Technology Inc.

DS41412F-page 343

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 FVREN bit of
the VREFCON0 register.

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: 

, 

 and 

.

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

 for the minimum delay requirement.

to Comparators, DAC

  x1
  x2
  x4

+

-

FVREN

FVRST

2

FVRS<1:0>

to ADC module

  x1
  x2
  x4

FVR BUF1

FVR BUF2

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)