ICS843252AGLF データシートの表示（PDF） - Integrated Circuit Systems

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ICS843252AGLF

FEMTOCLOCKS™ CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER

Integrated Circuit Systems 

Integrated

Circuit

Systems, Inc.

PRELIMINARY

ICS843252

FEMTOCLOCKS™CRYSTAL-TO-3.3V LVPECL

FREQUENCY SYNTHESIZER

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 4.

VCC

Q1

VOUT

RL

50

VCC - 2V

FIGURE 4. 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.

CC

• For logic high, V = V

=V

– 0.9V

OUT

OH_MAX

CC_MAX

(V

- V ) = 0.9V

CCO_MAX OH_MAX

• For logic low, V = V

=V

– 1.7V

OUT

OL_MAX

CC_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

CC_MAX

L

CC_MAX OH_MAX

CC_MAX

OH_MAX

L

CC_MAX OH_MAX

[(2V - 0.9V)/50Ω] * 0.9V = 19.8mW

Pd_L = [(V – (V - 2V))/R ] * (V - V ) = [(2V - (V

- V ))/R ] * (V - V ) =

OL_MAX

CC_MAX

L

CC_MAX OL_MAX

CC_MAX

OL_MAX

L

CC_MAX OL_MAX

[(2V - 1.7V)/50Ω] * 1.7V = 10.2mW

Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW

843252AG

www.icst.com/products/hiperclocks.html

12

REV. A NOVEMBER 9, 2005

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