Z8F082ASH020SC datasheet(185/244 Pages) ZILOG

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PS024705-0405

P R E L I M I N A R Y

Crystal Oscillator

Z8 Encore! XP® F08xA Series

Product Specification

167

Oscillator Operation with an External RC Network

Figure 26 illustrates a recommended configuration for connection with an external resis-

tor-capacitor (RC) network.

Figure 26.Connecting the On-Chip Oscillator to an External RC Network

An external resistance value of 45K

Ω is recommended for oscillator operation with an

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

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

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

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 20pF are recommended.

XIN

VDD

Oscillator Frequency (kHz)

×10

0.4

()

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