Datasheet

2011 Microchip Technology Inc. DS39932D-page 407
PIC18F46J11 FAMILY
26.3 On-Chip Voltage Regulator
The digital core logic of the PIC18F46J11 family
devices is designed on an advanced manufacturing
process, which requires 2.0V to 2.7V. The digital core
logic obtains power from the V
DDCORE/VCAP power
supply pin.
However, in many applications it may be inconvenient
to run the I/O pins at the same core logic voltage, as it
would restrict the ability of the device to interface with
other, higher voltage devices, such as those run at a
nominal 3.3V. Therefore, all PIC18F46J11 family
devices implement a dual power supply rail topology.
The core logic obtains power from the V
DDCORE/VCAP
pin, while the general purpose I/O pins obtain power
from the V
DD pin of the microcontroller, which may be
supplied with a voltage between 2.15V to 3.6V (“F”
devices) or 2.0V to 3.6V (“LF” devices).
This dual supply topology allows the microcontroller to
interface with standard 3.3V logic devices, while
running the core logic at a lower voltage of nominally
2.5V.
In order to make the microcontroller more convenient to
use, an integrated 2.5V low dropout, low quiescent
current linear regulator has been integrated on the die
inside PIC18F46J11 family devices. This regulator is
designed specifically to supply the core logic of the
device. It allows PIC18F46J11 family devices to
effectively run from a single power supply rail, without
the need for external regulators.
The on-chip voltage regulator is always enabled on “F”
devices. The V
DDCORE/VCAP pin serves simultaneously
as the regulator output pin and the core logic supply
power input pin. A capacitor should be connected to the
V
DDCORE/VCAP pin to ground and is necessary for regu-
lator stability. For example connections for PIC18F and
PIC18LF devices, see Figure 26-2.
On “LF” devices, the on-chip regulator is always
disabled. This allows the device to save a small amount
of quiescent current consumption, which may be
advantageous in some types of applications, such as
those which will entirely be running at a nominal 2.5V.
On PIC18LF46J11 family devices, the V
DDCORE/VCAP
pin still serves as the core logic power supply input pin,
and therefore, must be connected to a 2.0V to 2.7V
supply rail at the application circuit board level. On
these devices, the I/O pins may still optionally be sup-
plied with a voltage between 2.0V to 3.6V, provided that
V
DD is always greater than, or equal to,
V
DDCORE/VCAP. For example connections for PIC18F
and PIC18LF devices, see Figure 26-2.
The specifications for core voltage and capacitance are
listed in Section 29.3 “DC Characteristics:
PIC18F46J11 Family (Industrial)”.
26.3.1 VOLTAGE REGULATOR TRACKING
MODE AND LOW-VOLTAGE
DETECTION
When it is enabled, the on-chip regulator provides a con-
stant 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.
When the V
DD
supply input voltage drops too low to
regulate to 2.5V, the regulator enters Tracking mode. In
Tracking mode, the regulator output follows VDD, with a
typical voltage drop of 100 mV or less.
The on-chip regulator includes a simple, Low-Voltage
Detect (LVD) circuit. This circuit is separate and inde-
pendent of the High/Low-Voltage Detect (HLVD) module
described in Section 24.0 “High/Low Voltage Detect
(HLVD)”. The on-chip regulator LVD circuit continuously
monitors the V
DDCORE voltage level and updates the
LVDSTAT bit in the WDTCON register. The LVD detect
threshold is set slightly below the normal regulation set
point of the on-chip regulator.
Application firmware may optionally poll the LVDSTAT
bit to determine when it is safe to run at the maximum
rated frequency, so as not to inadvertently violate the
voltage versus frequency requirements provided by
Figure 29-1.
The V
DDCORE monitoring LVD circuit is only active
when the on-chip regulator is enabled. On “LF”
devices, the Analog-to-Digital Converter and the HLVD
module can still be used to provide firmware with V
DD
and VDDCORE voltage level information.
Note 1: The on-chip voltage regulator is only
available in parts designated with an “F”,
such as PIC18F25J11. The on-chip
regulator is disabled on devices with “LF”
in their part number.
2: The V
DDCORE/VCAP pin must never be
left floating. On “F” devices, it must be
connected to a capacitor, of size CEFC, to
ground. On “LF” devices, V
DDCORE/VCAP
must be connected to a power supply
source between 2.0V and 2.7V.
Note: In parts designated with an “LF”, such as
PIC18LF46J11, V
DDCORE must never
exceed V
DD.