Z8 Encore! XP® 4K Series
Product Specification
188
VDD
R
C
XIN
Figure 28.Connecting the On-Chip Oscillator to an External RC Network
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:
1×106
Oscillator Frequency (kHz) = ---------------------------------------------------------
(0.4 × R × C) + (4 × C)
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 KΩ 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.
PS022815-0206
Crystal Oscillator
ZILOG [ ZILOG, INC. ]
