ICS843022 datasheet(7/13 Pages) ICST

7 / 13 page

843022AG

www.icst.com/products/hiperclocks.html

REV. A NOVEMBER 30, 2004

Integrated

Circuit

Systems, Inc.

ICS843022

FEMTOCLOCKS™CRYSTAL-TO-

3.3V LVPECL CLOCK GENERATOR

PRELIMINARY

APPLICATION INFORMATION

Figure 2. CRYSTAL INPUt INTERFACE

CRYSTAL INPUT INTERFACE

The ICS843022 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 ICS843022 provides sepa-

rate power supplies to isolate any high switching

noise from the outputs to the internal PLL. V

CC, and VCCA should

individually

connected

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 1 illustrates how

a 10

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

capacitor should be connected to each V

CCA pin.

POWER SUPPLY FILTERING TECHNIQUES

FIGURE 1. POWER SUPPLY FILTERING

Ω

CCA

µF

.01

µF

3.3V

.01

µF

33p

18pF Parallel Crystal

27p

XTAL_OUT

XTAL_IN

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