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ICS843246BGI REV. A AUGUST 2, 2007

ICS843246I

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

Figure 5 shows an example of ICS843246I application sche-

matic. In this example, the device is operated at V

18pF parallel resonant 25MHz crystal is used. The C1 = 22pF

and C2 = 22pF are recommended for frequency accuracy. For

different board layout, the C1 and C2 may be slightly adjusted

for optimizing frequency accuracy. Two examples of LVPECL

termination are shown in this schematic. Additional termination

approaches are shown in the LVPECL Termination Application

Note.

C5

0.1uF

C4

0.01u

N_SEL0

Zo = 50 Ohm

VCC

(U1-2)

18pF

R6

82.5

RU2

Not Install

RU1

1K

Zo = 50 Ohm

C1

22pF

VCCO=3.3V

R4

82.5

RD2

1K

Set Logic

Input to

'1'

VCCO

C7

0.1uF

Set Logic

Input to

'0'

VCC

3.3V

C3

10uF

VCC=3.3V

R9

50

R3

133

R8

50

Optional

Y-Termination

VDD

C6

0.1uF

(U1-11)

RD1

Not Install

To Logic

Input

pins

R2

10

X1

25MHz

Zo = 50 Ohm

U1

843246I

VCC

VCCO

Zo = 50 Ohm

To Logic

Input

pins

N_SEL1

PLL_BY PASS

R5

133

(U1-1)

VDD

+

-

R7

50

+

-

C2

22pF

Logic Control Input Examples

FB_SEL

VCCA

EXPOSED PAD

Expose Metal Pad

(GROUND PAD)

GROUND PLANE

SOLDER

SIGNAL

TRACE

SIGNAL

TRACE

THERM AL VIA

SOLDER M ASK

The expose metal pad provides heat transfer from the device

to the P.C. board. The expose metal pad is ground pad

connected to ground plane through thermal via. The exposed

pad on the device to the exposed metal pad on the PCB is

contacted through solder as shown in Figure 4. For further

information, please refer to the Application Note on Surface

Mount Assembly of Amkor’s Thermally /Electrically Enhance

Leadframe Base Package, Amkor Technology.