ICS843034A01 datasheet(16/22 Pages) ICST

16 / 22 page

843034AY-01

www.icst.com/products/hiperclocks.html

REV. C NOVEMBER 28, 2005

Integrated

Circuit

Systems, Inc.

ICS843034-01

FEMTOCLOCKS™

MULTI-RATE LVPECL FREQUENCY SYNTHESIZER

PRELIMINARY

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 termina-

tion for LVPECL outputs. The two different layouts mentioned

are recommended only as guidelines.

FOUTx and nFOUTx are low impedance follower outputs that

generate ECL/LVPECL compatible outputs.Therefore, terminat-

ing resistors (DC current path to ground) or current sources

must be used for functionality. These outputs are designed to

FIGURE 6B. LVPECL OUTPUT TERMINATION

FIGURE 6A. LVPECL OUTPUT TERMINATION

drive 50

Ω transmission lines. Matched impedance techniques

should be used to maximize operating frequency and minimize

signal distortion. Figures 6A and 6B 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.

TERMINATION FOR 3.3V LVPECL OUTPUT

INPUTS:

CRYSTAL INPUT:

For applications not requiring the use of the crystal oscillator

input, both XTAL_IN and XTAL_OUT can be left floating.

Though not required, but for additional protection, a 1k

resistor can be tied from XTAL_IN to ground.

CLK INPUT:

For applications not requiring the use of a clock input, it can

be left floating. Though not required, but for additional

protection, a 1k

Ω resistor can be tied from the CLK input to

ground.

CLK/nCLK INPUT:

For applications not requiring the use of the differential input,

both CLK and nCLK can be left floating. Though not required,

but for additional protection, a 1k

Ω resistor can be tied from

CLK to ground.

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:

LVCMOS OUTPUT:

All unused LVCMOS output can be left floating. We

recommend that there is no trace attached.

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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