ICS853111B datasheet(14/19 Pages) IDT

14 / 19 page

IDT™ / ICS™

1-TO-10, LVPECL/ECL FANOUT BUFFER

ICS853111BY REV. B SEPTEMBER 5, 2007

ICS853111B

LOW SKEW, 1-TO-10, DIFFERENTIAL-TO-2.5V, 3.3V LVPECL/ECL 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 7.

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

voltage of V

CCO

- 2V.

•

For logic high, V

OUT = VOH_MAX = VCCO_MAX – 0.935V

CC_MAX

- V

OH_MAX

) = 0.935V

•

For logic low, V

OUT = VOL_MAX = VCCO_MAX – 1.67V

CCO_MAX

- V

OL_MAX

) = 1.67V

Pd_H = [(V

OH_MAX

– (V

CCO_MAX

- 2V))/R

] * (V

CCO_MAX

- V

OH_MAX

) = [(2V - (V

CCO_MAX

- V

OH_MAX

))/R

] * (V

CCO _MAX

- V

OH_MAX

) =

[(2V - 0.935V)/50Ω] * 0.935V = 19.92mW

Pd_L = [(V

OL_MAX

– (V

CCO_MAX

- 2V))/R

] * (V

CCO_MAX

- V

OL_MAX

) = [(2V - (V

CCO_MAX

- V

OL_MAX

))/R

] * (V

CCO_MAX

- V

OL_MAX

) =

[(2V - 1.67V)/50Ω] * 1.67V = 11.02mW

Total Power Dissipation per output pair = Pd_H + Pd_L = 30.94mW

OUT

CCO

CCO - 2V

FIGURE 7. LVPECL DRIVER CIRCUIT AND TERMINATION

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