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ICS843246BGI REV. A AUGUST 2, 2007

ICS843246I

FEMTOCLOCKS™ CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER W/FANOUT BUFFER

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

are vulnerable to random noise. The ICS843246I provides

separate power supplies to isolate any high switching

noise from the outputs to the internal PLL. V

V

through vias, and bypass capacitors should be used for each

pin. To achieve optimum jitter performance, power supply iso-

lation is required. Figure 1 illustrates how a 10

Ω resistor along

with a 10

μF and a .01μF bypass capacitor should be connected

to each V

10

Ω

V

CCA

10

μF

.01

μF

3.3V

.01

μF

V

CC

The ICS843246I has been characterized with 18pF parallel

resonant crystals. The capacitor values shown in Figure 2

below were deter mined using an 18pF parallel resonant

crystal and were chosen to minimize the ppm error.

C1

22p

X1

18pF Parallel Crystal

C2

22p

XTAL_OUT

XTAL_IN

All control pins have internal pull-ups or pull-downs; additional

resistance is not required but can be added for additional

protection. A 1k

Ω resistor can be used.

All unused LVPECL outputs can be left floating. We recommend

that there is no trace attached. Both sides of the differential output

pair should either be left floating or terminated.