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ICS84324

CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER WITH FANOUT BUFFER

Integrated Circuit Systems 

Integrated

Circuit

Systems, Inc.

PRELIMINARY

ICS84324

CRYSTAL-TO-3.3V LVPECL

FREQUENCY SYNTHESIZER WITH FANOUT BUFFER

3. Calculations and Equations.

The purpose of this section is to derive the power dissipated into the load.

LVPECL output driver circuit and termination are shown in Figure 6.

VCCO

Q1

VOUT

RL

50

VCCO - 2V

FIGURE 6. LVPECL DRIVER CIRCUIT AND TERMINATION

To calculate worst case power dissipation into the load, use the following equations which assume a 50Ω load, and a termination

voltage of V - 2V.

CCO

• For logic high, V = V

=V

– 1.0V

OUT

OH_MAX

CCO_MAX

(V

- V ) = 1.0V

CCO_MAX OH_MAX

• For logic low, V = V = V

– 1.7V

OUT

OL_MAX

CCO_MAX

(V

- V ) = 1.7V

CCO_MAX OL_MAX

Pd_H is power dissipation when the output drives high.

Pd_L is the power dissipation when the output drives low.

Pd_H = [(V – (V

- 2V))/R ] * (V

- V ) = [(2V - (V

- V ))/R ] * (V

-V )=

OH_MAX

CCO_MAX

L

CCO_MAX OH_MAX

CCO_MAX

OH_MAX

L

CCO_MAX OH_MAX

[(2V - 1V)/50Ω) * 1V = 20.0mW

Pd_L = [(V – (V

- 2V))/R ] * (V

- V ) = [(2V - (V

- V ))/R ] * (V

-V )=

OL_MAX

CCO_MAX

L

CCO_MAX OL_MAX

CCO_MAX

OL_MAX

L

CCO_MAX OL_MAX

[(2V - 1.7V)/50Ω) * 1.7V = 10.2mW

Total Power Dissipation per output pair = Pd_H + Pd_L = 30.2mW

84324EM

www.icst.com/products/hiperclocks.html

11

REV. A SEPTEMBER 18, 2003

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