PIC16CR74ESLASHSP datasheet(94/172 Pages) MICROCHIP

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PIC16CR7X

DS21993C-page 92

TABLE 12-2:

CAPACITOR SELECTION FOR

CRYSTAL OSCILLATOR

(FOR DESIGN GUIDANCE

ONLY)

12.2.3

RC OSCILLATOR

For timing insensitive applications, the “RC” device

option offers additional cost savings. The RC oscillator

frequency is a function of the supply voltage, the resis-

tor (REXT) and capacitor (CEXT) values, and the operat-

ing temperature. In addition to this, the oscillator

frequency will vary from unit to unit due to normal

process parameter variation. Furthermore, the differ-

ence in lead frame capacitance between package

types

will

also

affect

the

oscillation

frequency,

especially for low CEXT values. The user also needs to

take into account variation due to tolerance of external

R and C components used. Figure 12-3 shows how the

R/C combination is connected to the PIC16CR7X.

FIGURE 12-3:

RC OSCILLATOR MODE

Osc Type

Crystal

Freq.

Typical Capacitor Values

Tested:

32 kHz

33 pF

200 kHz

15 pF

200 kHz

56 pF

1 MHz

15 pF

4 MHz

15 pF

4 MHz

15 pF

8 MHz

15 pF

20 MHz

15 pF

Capacitor values are for design guidance only.

These capacitors were tested with the crystals listed

below for basic start-up and operation. These values

were not optimized.

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.

See the notes following this table for additional

information.

Crystals Used:

32 kHz

Epson C-001R32.768K-A

200 kHz

STD XTL 200.000KHz

1 MHz

ECS ECS-10-13-1

4 MHz

ECS ECS-40-20-1

8 MHz

EPSON CA-301 8.000M-C

20 MHz

EPSON CA-301 20.000M-C

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 compo-

nents.

3: Rs may be required in HS mode, as well

as XT mode, 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.

OSC2/CLKOUT

CEXT

REXT

PIC16CR7X

OSC1

FOSC/4

Internal

Clock

VDD

VSS

Recommended values:

3 k

Ω ≤ REXT ≤ 100 kΩ

CEXT > 20pF

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