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.
VDD
R
XIN
C
Figure 26.Connecting the On-Chip Oscillator to an External RC Network
An external resistance value of 45KΩ is recommended for oscillator operation with an
external RC network. The minimum resistance value to ensure operation is 40KΩ. 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:
1×106
(0.4 × R × C) + (4 × C)
---------------------------------------------------------
Oscillator Frequency (kHz) =
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 45KΩ 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.
PS024705-0405
P R E L I M I N A R Y
Crystal Oscillator
ZILOG [ ZILOG, INC. ]
