Z8F1680SH020SG Datasheet, PDF (349/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
324
An external resistance value of 45 KΩ is recommended for oscillator operation with an
external RC network. The minimum resistance value to ensure operation is 40 KΩ. The
typical oscillator frequency can be estimated from the values of the resistor (R in KΩ) and
capacitor (C in pF) elements using the following equation:
Oscillator Frequency (kHz) = _---0---.-4-----_-----_R-----1-_--^--_C--1---0_---6-+-----_--4----_-----_C-----_
Figure 64 displays the typical (3.3 V and 25° C) oscillator frequency as a function of the
capacitor (C in pF) employed in the RC network assuming a 45 KΩ external resistor. For
very small values of C, the parasitic capacitance of the oscillator X_IN pin and the printed
circuit board should be included in the estimation of the oscillator frequency.
It is possible to operate the RC oscillator using only the parasitic capacitance of the pack-
age and printed circuit board. To minimize sensitivity to external parasitics, external
capacitance values in excess of 20 pF are recommended.
4000
3750
3500
3250
3000
2750
2500
2250
2000
1750
1500
1250
1000
750
500
250
0
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500
C (pF)
Figure 64. Typical RC Oscillator Frequency as a Function of External Capacitance
PS025015-1212
PRELIMINARY
Crystal Oscillator