8430AY-51

www.icst.com/products/hiperclocks.html

REV. D FEBRUARY 11, 2003

9

PRELIMINARY

Integrated

Circuit

Systems, Inc.

ICS8430-51

The ICS8430-51 features an internal oscillator that uses an

external quartz crystal as the source of its reference frequency.

A 16MHz crystal divided by 16 before being sent to the phase

detector provides the 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 parallel resonant crystal in

series to pin 24.

Figure 4A shows how to interface with a crystal.

Figures 4A, 4B, and 4C show various crystal parameters

which are recommended only as guidelines.

Figure 4A shows

how to interface a capacitor with a parallel resonant crystal.

Figure 3B shows the capacitor value needed for the optimum

resonant crystals.

parallel resonant crystals.

14.318

15.000

16.667

24.000

19.440

20.000

0

10

20

30

40

50

60

14

15

16

17

18

19

20

21

22

23

24

25

Crystal Frequency (MHz)

-100

-80

-60

-40

-20

0

20

40

60

80

100

0

1020

30

4050

60

Series Capacitor, C1 (pF)

19.44MHz

16MHz

15.00MHz

As in any high speed analog circuitry, the power supply pins

are vulnerable to random noise. The ICS8430-51 provides

separate power supplies to isolate any high switching

noise from the outputs to the internal PLL. V

should be individually connected to the power supply

plane through vias, and bypass capacitors should be

used for each pin. To achieve optimum jitter performance,

power supply isolation is required.

Figure 3 illustrates how

a 10

Ω resistor along with a 10µF and a .01µF bypass

capacitor should be connected to each V

10

Ω

V

CCA

10

µF

.01

µF

3.3V

.01

µF

V

CC

Optional

XTAL2

(Pin 25, LQFP)

XTAL1

(Pin 24, LQFP)

ICS8430-51

ppm performance over various parallel resonant crystals.

Figure 4C shows the recommended tuning capacitance for

various parallel resonant crystals.