Datasheet
PIC18F87K90 FAMILY
DS39957D-page 442 2009-2011 Microchip Technology Inc.
28.3 On-Chip Voltage Regulator
All of the PIC18F87K90 family devices power their core
digital logic at a nominal 3.3V. For designs that are
required to operate at a higher typical voltage, such as
5V, all family devices incorporate two on-chip regula-
tors that allow the device to run its core logic from V
DD.
Those regulators are:
• Normal On-Chip Regulator
• Ultra Low-Power, On-Chip Regulator
The hardware configuration of these regulators is the
same and is explained in
Section 28.3.1 “Regulator
Enable/disable by Hardware”
. The regulators’ only
differences relate to when the device enters Sleep, as
explained in
Section 28.3.2.
28.3.1 REGULATOR ENABLE/DISABLE BY
HARDWARE
The regulator can be enabled or disabled only by
hardware. The regulator is controlled by the ENVREG
pin and the V
DDCORE/VCAP pin.
28.3.1.1 Regulator Enable Mode
Tying VDD 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
DDCORE/VCAP pin (see
Figure 28-2). This helps maintain the regulator’s
stability. The recommended value for the filter capacitor
is given in
Section 31.2 DC Characteristics.
28.3.1.2 Regulator Disable Mode
If ENVREG is tied to VSS, the regulator is disabled. In
this case, a 0.1
F capacitor should be connected to
the V
DDCORE/VCAP pin (see Figure 28-2).
When the regulator is being used, the overall voltage
budget is very tight. The regulator should operate the
device down to 1.8V. When V
DD drops below 3.3V, the
regulator no longer regulates, but the output voltage fol-
lows the input until V
DD reaches 1.8V. Below this voltage,
the output of the regulator output may drop to 0V.
FIGURE 28-2: CONNECTIONS FOR THE
ON-CHIP REGULATOR
VDD
ENVREG
V
DDCORE/VCAP
VSS
CF
5V
Regulator Enabled (ENVREG tied to VDD):
Regulator Disabled (ENVREG tied to V
SS):
Note 1:
These are typical operating voltages. For the
full operating ranges of V
DD and VDDCORE,
see
Section 31.2 “DC Characteristics”.
PIC18F87K90
VDD
ENVREG
V
DDCORE/VCAP
V
SS
3.3V
(1)
PIC18F87K90
0.1 F