84021AY

www.icst.com/products/hiperclocks.html

REV. A NOVEMBER 7, 2003

11

Integrated

Circuit

Systems, Inc.

ICS84021

The ICS84021 has been characterized with 18pF parallel

resonant crystals. The capacitor values, C1 and C2, shown

in

Figure 3 below were determined using a 25MHz, 18pF

parallel resonant crystal and were chosen to minimize the

ppm error. The optimum C1 and C2 values can be slightly

adjusted for different board layouts.

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

are vulnerable to random noise. The ICS84021 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 2 illustrates how

a 24

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

capacitor should be connected to each V

24

Ω

V

DDA

10

µF

.01

µF

3.3V

.01

µF

V

DD

C1

22p

X1

18pF Parallel Cry stal

C2

22p

XTAL2

XTAL1