PIC18F87K90 Datasheet, PDF (45/566 Pages) Microchip Technology – 64/80-Pin, High-Performance Microcontrollers with LCD Driver and nanoWatt XLP Technology

PIC18F87K90 FAMILY
TABLE 3-2:
CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Typical Capacitor Values Used:
Mode
Freq.
OSC1
OSC2
HS
8.0 MHz
16.0 MHz
27 pF
22 pF
27 pF
22 pF
Capacitor values are for design guidance only.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
VDD and temperature range for the application. Refer
to the following application notes for oscillator-specific
information:
• AN588, “PIC^® Microcontroller Oscillator Design
Guide”
• AN826, “Crystal Oscillator Basics and Crystal
Selection for rfPIC^® and PIC^® Devices”
• AN849, “Basic PIC^® Oscillator Design”
• AN943, “Practical PIC^® Oscillator Analysis and
Design”
• AN949, “Making Your Oscillator Work”
See the notes following Table 3-3 for additional
information.
TABLE 3-3:
CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc Type
Crystal
Freq.
Typical Capacitor Values
Tested:
C1
C2
HS
4 MHz
27 pF
27 pF
8 MHz
22 pF
22 pF
20 MHz
15 pF
15 pF
Capacitor values are for design guidance only.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
VDD and temperature range for the application.
Refer to the Microchip application notes cited in
Table 3-2 for oscillator-specific information. Also see
the notes following this table for additional
information.
Note 1: Higher capacitance increases the stability
of oscillator but also increases the start-up
time.
2: Since each resonator/crystal has its own
characteristics, the user should consult
the resonator/crystal manufacturer for
appropriate values of external
components.
3: Rs may be required to avoid overdriving
crystals with low drive level specification.
4: Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
FIGURE 3-2:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS OR HSPLL
CONFIGURATION)
C1⁽¹⁾
OSC1
XTAL
C2⁽¹⁾
OSC2
RS⁽²⁾
RF⁽³⁾
To
Internal
Logic
Sleep
PIC18F87K90
Note 1:
2:
3:
See Table 3-2 and Table 3-3 for initial values of
C1 and C2.
A series resistor (RS) may be required for AT
strip cut crystals.
RF varies with the oscillator mode chosen.
3.5 RC Oscillator
For timing-insensitive applications, the RC and RCIO
Oscillator modes offer additional cost savings. The
actual oscillator frequency is a function of several
factors:
• Supply voltage
• Values of the external resistor (REXT) and
capacitor (CEXT)
• Operating temperature – Given the same device,
operating voltage and temperature and
component values, there will also be unit-to-unit
frequency variations. These are due to factors
such as:
- normal manufacturing variation
- difference in lead frame capacitance between
package types (especially for low CEXT
values)
- variations within the tolerance of limits of
REXT and CEXT
 2010 Microchip Technology Inc.
Preliminary
DS39957B-page 45