ICS84021 datasheet(11/14 Pages) ICST

11 / 14 page

84021AY

www.icst.com/products/hiperclocks.html

REV. A NOVEMBER 7, 2003

Integrated

Circuit

Systems, Inc.

ICS84021

260MHZ, CRYSTAL-TO-LVCMOS / LVTTL

FREQUENCY SYNTHESIZER

CRYSTAL INPUT INTERFACE

The ICS84021 has been characterized with 18pF parallel

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

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

Figure 3. CRYSTAL INPUt INTERFACE

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.

APPLICATION INFORMATION

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

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 2 illustrates how

a 24

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

capacitor should be connected to each V

DDA pin.

FIGURE 2. POWER SUPPLY FILTERING

Ω

DDA

µF

.01

µF

3.3V

.01

µF

POWER SUPPLY FILTERING TECHNIQUES

22p

18pF Parallel Cry stal

22p

XTAL2

XTAL1

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