84329AV

www.icst.com/products/hiperclocks.html

REV. D DECEMBER 15, 2004

10

Integrated

Circuit

Systems, Inc.

ICS84329

The ICS84329 features an internal oscillator that uses an external

quartz crystal as the source of its reference frequency. The

oscillator is a series resonant, multi-vibrator type design. This

design provides better stability and eliminates the need for large

on chip capacitors.Though a series resonant crystal is preferred,

a parallel resonant crystal can be used. A parallel resonant mode

crystal used in a series resonant circuit will exhibit a frequency

of oscillation a few hundred ppm lower than specified. A few

hundred ppm translates to KHz inaccuracy. In general computing

applications, this level of inaccuracy is irrelevant. If better ppm

accuracy is required, an external capacitor can be added to a

quartz crystal in series to XTAL_IN.

Figure 5A shows how to

interface with a crystal.

Figures 5A and 5B show various crystal parameters which are

recommended only as guidelines.

Figure 5A shows how to inter-

face a capacitor with a parallel resonant crystal.

Figure 5B shows

the capacitor value needed for the optimum ppm performance

over various series resonant crystal frequencies. For IA64/32

platforms which required a Raltron Parallel Resonant Quartz

crystal part #AS-16.66-18-SMD-T-M1, a 7pF series capacitor can

be used to better the ppm accuracy.

NOTE: For crystal frequencies higher than 17MHz,

a series tuning capacitor is required for proper operation.

XTAL_OUT

XTAL_IN

ICS84329

resonant crystals.

10.000

14.318

12.000

24.000

20.000

16.000

0

5

10

15

20

25

30

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

Series Resonant Crystal Frequency (MHz)