PIC18F87K90 Datasheet, PDF (440/566 Pages) Microchip Technology – 64/80-Pin, High-Performance Microcontrollers with LCD Driver and nanoWatt XLP Technology

PIC18F87K90 FAMILY
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 allows the device to run its core logic from
VDD. Those regulators are:
• Normal On-Chip Regulator
• Ultra Low-Power, On-Chip Regulator
The hardware configuration of these regulators are the
same and are explained in Section 28.3.1. The regula-
tors’ 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 VDDCORE/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 VDD pins.
When the regulator is enabled, a low-ESR filter capac-
itor must be connected to the VDDCORE/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 VDDCORE/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 VDD drops below 3.3V, the
regulator no longer regulates, but the output voltage fol-
lows the input until VDD 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
Regulator Enabled (ENVREG tied to VDD):
5V
PIC18F87K90
VDD
ENVREG
VDDCORE/VCAP
CF
VSS
Regulator Disabled (ENVREG tied to VSS):
3.3V⁽¹⁾
PIC18F87K90
VDD
ENVREG
0.1 F
VDDCORE/VCAP
VSS
Note 1:
These are typical operating voltages. For the
full operating ranges of VDD and VDDCORE,
see Section 31.2 DC Characteristics.
DS39957B-page 440
Preliminary
 2010 Microchip Technology Inc.