Z8F021ASH020SC datasheet(207/276 Pages) ZILOG

207 / 276 page

PS022815-0206

Crystal Oscillator

Z8 Encore! XP® 4K Series

Product Specification

188

Figure 28.Connecting the On-Chip Oscillator to an External RC Network

An external resistance value of 45 K

Ω is recommended for oscillator operation with an

external RC network. The minimum resistance value to ensure operation is 40 K

Ω. The

typical oscillator frequency can be estimated from the values of the resistor (R in K

Ω) and

capacitor (C in pF) elements using the following equation:

Figure 29 illustrates the typical (3.3 V and 250C) oscillator frequency as a function of the

capacitor (C in pF) employed in the RC network assuming a 45 K

Ω external resistor. For

very small values of C, the parasitic capacitance of the oscillator XIN 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.

XIN

VDD

Oscillator Frequency (kHz)

×10

0.4 RC

()

4 C

()

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Z8F021ASH020SC 数据表(PDF) 207 Page - Zilog, Inc.