ICS843246AM datasheet(9/15 Pages) ICST

9 / 15 page

843246AM

www.icst.com/products/hiperclocks.html

REV. A SEPTEMBER 29, 2005

Integrated

Circuit

Systems, Inc.

ICS843246

FEMTOCLOCKS™CRYSTAL-TO-3.3V LVPECL

FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER

PRELIMINARY

TERMINATION FOR 3.3V LVPECL OUTPUT

CC - 2V

RTT

o = 50Ω

FOUT

FIN

RTT =

((V

OH + VOL) / (VCC – 2)) – 2

3.3V

125

o = 50Ω

FOUT

FIN

The clock layout topology shown below is a typical termi-

nation for LVPECL outputs. The two different layouts men-

tioned are recommended only as guidelines.

FOUT and nFOUT are low impedance follower outputs that

generate ECL/LVPECL compatible outputs. Therefore, termi-

nating resistors (DC current path to ground) or current

sources must be used for functionality. These outputs are

FIGURE 3B. LVPECL OUTPUT TERMINATION

FIGURE 3A. LVPECL OUTPUT TERMINATION

designed to drive 50

Ω transmission lines. Matched imped-

ance techniques should be used to maximize operating

frequency and minimize signal distortion. Figures 3A and

3B show two different layouts which are recommended only

as guidelines. Other suitable clock layouts may exist and it

would be recommended that the board designers simulate to

guarantee compatibility across all printed circuit and clock

component process variations.

INPUTS:

LVCMOS CONTROL PINS:

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.

RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS

OUTPUTS:

LVPECL OUTPUT

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.

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