
2002 Microchip Technology Inc.
DS41120B-page 103
PIC16C717/770/771
10.1
Bandgap Voltage Reference
The bandgap module generates a stable voltage refer-
ence of over a range of temperatures and device sup-
ply voltages. This module is enabled anytime any of the
following are enabled:
Brown-out Reset
Low-voltage Detect
Either of the internal analog references (VRH,
VRL)
Whenever the above are all disabled, the bandgap
module is disabled and draws no current.
10.2
Internal VREF for A/D Converter
The bandgap output voltage is used to generate two
stable references for the A/D converter module. These
references are enabled in software to provide the user
with the means to turn them on and off in order to min-
imize current consumption. Each reference can be indi-
vidually enabled.
The VRH reference is enabled with control bit VRHEN
(REFCON<7>). When this bit is set, the gain amplifier
is enabled. After a specified start-up time a stable ref-
erence of 4.096V nominal is generated and can be
used by the A/D converter as a reference input.
The VRL reference is enabled by setting control bit
VRLEN (REFCON<6>). When this bit is set, the gain
amplifier is enabled. After a specified start-up time a
stable reference of 2.048V nominal is generated and
can be used by the A/D converter as a reference input.
Each voltage reference is available for external use via
VRL and VRH pins.
Each reference, if enabled, can be output on an exter-
nal pin by setting the VRHOEN (high reference output
enable) or VRLOEN (low reference output enable) con-
trol bit. If the reference is not enabled, the VRHOEN
and VRLOEN bits will have no effect on the corre-
sponding pin. The device specific pin can then be used
as general purpose I/O.
FIGURE 10-1: BLOCK DIAGRAM OF LVD AND VOLTAGE REFERENCE CIRCUIT
Note:
If VRH or VRL is enabled and the other ref-
erence (VRL or VRH), the BOR, and the
LVD modules are not enabled, the band-
gap will require a start-up time before the
bandgap reference is stable. Before using
the internal VRH or VRL reference, ensure
that the bandgap reference voltage is sta-
ble by monitoring the BGST bit in the LVD-
CON register. The voltage references will
not be reliable until the bandgap is stable
as shown by BGST being set.
VDD
generates
16
t
o
1
M
U
X
BGAP
VRH
VRL
LVDEN
LVDCON
REFCON
BODEN
LVDEN
VRHEN + VRLEN
RA1/AN1/LVDIN
LVDIF