ICS858012 datasheet(12/15 Pages) ICST

12 / 15 page

858012AK

www.icst.com/products/hiperclocks.html

REV. A NOVEMBER 28, 2005

Integrated

Circuit

Systems, Inc.

ICS858012

LOW SKEW, 1-TO-2, DIFFERENTIAL-TO-

2.5V, 3.3V LVPECL FANOUT BUFFER

PRELIMINARY

3. Calculations and Equations.

LVPECL output driver circuit and termination are shown in Figure 7.

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

Ω load, and a termination

voltage of V

- 2V.

•

For logic high, V

OUT

= V

OH_MAX

= V

CC_MAX

– 0.895V

CC_MAX

- V

OH_MAX

) = 0.895V

•

For logic low, V

OUT

= V

OL_MAX

= V

CC_MAX

– 1.695V

CC_MAX

- V

OL_MAX

) = 1.695V

Pd_H is power dissipation when the output drives high.

Pd_L is the power dissipation when the output drives low.

Pd_H = [(V

OH_MAX

– (V

CC_MAX

- 2V))/R

] * (V

CC_MAX

- V

OH_MAX

) = [(2V - (V

CC_MAX

- V

OH_MAX

))/R

] * (V

CC_MAX

- V

OH_MAX

) =

[(2V - 0.895V)/50

Ω] * 0.895V = 19.78mW

Pd_L = [(V

OL_MAX

– (V

CC_MAX

- 2V))/R

] * (V

CC_MAX

- V

OL_MAX

) = [(2V - (V

CC_MAX

- V

OL_MAX

))/R

] * (V

CC_MAX

- V

OL_MAX

) =

[(2V - 1.695V)/50

Ω] * 1.695V = 10.34mW

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

FIGURE 7. LVPECL DRIVER CIRCUIT ANDTERMINATION

VOUT

VCC - 2V

VCC

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