PIC18F67J11T-I Datasheet, PDF (341/466 Pages) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Flash Microcontrollers

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 VDD.
The regulator is controlled by the ENVREG pin. Tying
VDD to the pin enables the regulator, which in turn,
provides power to the core from the other VDD pins.
When the regulator is enabled, a low-ESR filter capac-
itor must be connected to the VDDCORE/VCAP pin
(Figure 25-2). This helps to maintain the stability of the
regulator. The recommended value for the filter capac-
itor is provided in Section 28.3 “DC Characteristics:
PIC18F87J11 Family (Industrial)”.
If ENVREG is tied to VSS, 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
VDDCORE/VCAP pin to run the I/O pins at higher voltage
levels, typically 3.3V. Alternatively, the VDDCORE/VCAP
and VDD pins can be tied together to operate at a lower
nominal voltage. Refer to Figure 25-2 for possible
configurations.
25.3.1
VOLTAGE REGULATOR TRACKING
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 VDD of
about 2.5V, all the way up to the device’s VDDMAX. It
does not have the capability to boost VDD 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 VDD, with a typical voltage drop of
100 mV.
The on-chip regulator includes a simple, Low-Voltage
Detect (LVD) circuit. If VDD drops too low to maintain
approximately 2.45V on VDDCORE, 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 VDDCORE. Firmware can clear the interrupt flag, but
a new interrupt will not be generated until VDDCORE
rises back above, and then falls below, the 2.45 thresh-
old. Upon device Resets, the interrupt flag will reset to
‘0’, even if VDDCORE 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
VDDCORE.
FIGURE 25-2:
CONNECTIONS FOR THE
ON-CHIP REGULATOR
Regulator Enabled (ENVREG tied to VDD):
3.3V
PIC18F87J11
VDD
ENVREG
VDDCORE/VCAP
CF
VSS
Regulator Disabled (ENVREG tied to ground):
2.5V⁽¹⁾
3.3V⁽¹⁾
PIC18F87J11
VDD
ENVREG
VDDCORE/VCAP
VSS
Regulator Disabled (VDD tied to VDDCORE):
2.5V⁽¹⁾
PIC18F87J11
VDD
ENVREG
VDDCORE/VCAP
VSS
Note 1:
These are typical operating voltages. Refer
to Section 28.1 “DC Characteristics:
Supply Voltage” for the full operating
ranges of VDD and VDDCORE.
 2007-2012 Microchip Technology Inc.
DS39778E-page 341