840002AL datasheet(9/12 Pages) ICST

9 / 12 page

Integrated

Circuit

Systems, Inc.

840002AGI

www.icst.com/products/hiperclocks.html

REV. A MARCH 10, 2005

ICS840002I

FEMTOCLOCKS™CRYSTAL-TO-

LVCMOS/LVTTL FREQUENCY SYNTHESIZER

APPLICATION INFORMATION

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

are vulnerable to random noise. The ICS840002I provides

separate power supplies to isolate any high switching

noise from the outputs to the internal PLL. V

DD, VDDA, and VDDO

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 1 illustrates how

a 10

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

capacitor should be connected to each V

DDA.

POWER SUPPLY FILTERING TECHNIQUES

FIGURE 1. POWER SUPPLY FILTERING

DDA

μF

.01

μF

3.3V or 2.5V

.01

μF

CRYSTAL INPUT INTERFACE

The ICS840002I has been characterized with 18pF parallel

resonant crystals. The capacitor values shown in

Figure 2

Figure 2. CRYSTAL INPUt INTERFACE

below were determined using a 26.5625MHz 18pF parallel

resonant crystal and were chosen to minimize the ppm error.

ICS840002I

22p

18pF Parallel Crystal

22p

XTAL_OUT

XTAL_IN

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