Microchip Technology DV164136 Fiche De Données
2007-2012 Microchip Technology Inc.
DS39778E-page 341
PIC18F87J11 FAMILY
25.3
On-Chip Voltage Regulator
All of the PIC18F87J11 family devices power their core
digital logic at a nominal 2.5V. For designs that are
required to operate at a higher typical voltage, such as
3.3V, all devices in the PIC18F87J11 family incorporate
an on-chip regulator that allows the device to run its
core logic from V
digital logic at a nominal 2.5V. For designs that are
required to operate at a higher typical voltage, such as
3.3V, all devices in the PIC18F87J11 family incorporate
an on-chip regulator that allows the device to run its
core logic from V
DD
.
The regulator is controlled by the ENVREG pin. Tying
V
V
DD
to the pin enables the regulator, which in turn,
provides power to the core from the other V
DD
pins.
When the regulator is enabled, a low-ESR filter capac-
itor must be connected to the V
itor must be connected to the V
DDCORE
/V
CAP
pin
). This helps to maintain the stability of the
regulator. The recommended value for the filter capac-
itor is provided in
itor is provided in
If ENVREG is tied to V
SS
, the regulator is disabled. In
this case, separate power for the core logic at a nomi-
nal 2.5V must be supplied to the device on the
V
nal 2.5V must be supplied to the device on the
V
DDCORE
/V
CAP
pin to run the I/O pins at higher voltage
levels, typically 3.3V. Alternatively, the V
DDCORE
/V
CAP
and V
DD
pins can be tied together to operate at a lower
nominal voltage. Refer to
for possible
configurations.
25.3.1
VOLTAGE REGULATOR TRACKING
MODE AND LOW-VOLTAGE
DETECTION
MODE AND LOW-VOLTAGE
DETECTION
When it is enabled, the on-chip regulator provides a
constant voltage of 2.5V nominal to the digital core
logic. The regulator can provide this level from a V
constant voltage of 2.5V nominal to the digital core
logic. The regulator can provide this level from a V
DD
of
about 2.5V, all the way up to the device’s V
DDMAX
. It
does not have the capability to boost V
DD
levels below
2.5V. In order to prevent “brown-out” conditions, when
the voltage drops too low for the regulator, the regulator
enters Tracking mode. In Tracking mode, the regulator
output follows V
the voltage drops too low for the regulator, the regulator
enters Tracking mode. In Tracking mode, the regulator
output follows V
DD
, with a typical voltage drop of
100 mV.
The on-chip regulator includes a simple, Low-Voltage
Detect (LVD) circuit. If V
The on-chip regulator includes a simple, Low-Voltage
Detect (LVD) circuit. If V
DD
drops too low to maintain
approximately 2.45V on V
DDCORE
, the circuit sets the
Low-Voltage Detect Interrupt Flag, LVDIF (PIR2<2>).
This can be used to generate an interrupt and put the
application into a low-power operational mode, or
trigger an orderly shutdown. Low-Voltage Detection is
only available when the regulator is enabled.
The Low-Voltage Detect interrupt is edge-sensitive.
The interrupt flag will only be set once per falling edge
of V
This can be used to generate an interrupt and put the
application into a low-power operational mode, or
trigger an orderly shutdown. Low-Voltage Detection is
only available when the regulator is enabled.
The Low-Voltage Detect interrupt is edge-sensitive.
The interrupt flag will only be set once per falling edge
of V
DDCORE
. Firmware can clear the interrupt flag, but
a new interrupt will not be generated until V
DDCORE
rises back above, and then falls below, the 2.45 thresh-
old. Upon device Resets, the interrupt flag will reset to
‘0’, even if V
old. Upon device Resets, the interrupt flag will reset to
‘0’, even if V
DDCORE
is less than 2.45V. When the
regulator is enabled, the LVDSTAT bit in the WDTCON
register can be polled to determine the current level of
V
register can be polled to determine the current level of
V
DDCORE
.
FIGURE 25-2:
CONNECTIONS FOR THE
ON-CHIP REGULATOR
ON-CHIP REGULATOR
V
DD
ENVREG
V
DDCORE
/V
CAP
V
SS
PIC18F87J11
3.3V
(1)
2.5V
(1)
V
DD
ENVREG
V
DDCORE
/V
CAP
V
SS
PIC18F87J11
C
F
3.3V
Regulator Enabled (ENVREG tied to V
DD
):
Regulator Disabled (ENVREG tied to ground):
V
DD
ENVREG
V
DDCORE
/V
CAP
V
SS
PIC18F87J11
2.5V
(1)
Regulator Disabled (V
DD
tied to V
DDCORE
):
Note
1:
“DC Characteristics:
Supply Voltage”
for the full operating
ranges of V
DD
and V
DDCORE
.