840021AG

www.icst.com/products/hiperclocks.html

REV. A NOVEMBER 30, 2004

6

Integrated

Circuit

Systems, Inc.

ICS840021

The ICS840021 has been characterized with 18pF parallel

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

Figure 2 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 ICS840021 provides separate

power supplies to isolate any high switching noise from the out-

puts to the internal PLL. V

nected to the power supply plane through vias, and bypass ca-

pacitors should be used for each pin. To achieve optimum

jitter performance, power supply isolation is required.

Figure 1

illustrates how a 10

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

bypass capacitor should be connected to each V

10

Ω

V

DDA

10

µF

.01

µF

3.3V

.01

µF

V

DD

C1

33p

X1

18pF Parallel Crystal

C2

27p

XTAL_OUT

XTAL_IN