ICS853014BGL datasheet(15/19 Pages) IDT

15 / 19 page

ICS853014

LOW SKEW, 1-TO-5, DIFFERENTIAL-TO-2.5V, 3.3V LVPECL/ECL FANOUT BUFFER

IDT™ / ICS™ 2.5V, 3.3V LVPECL/ECL FANOUT BUFFER

ICS853014BG REV. DNOVEMBER 12, 2007

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.

Figure 7. 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 VCC – 2V.

•

For logic high, VOUT = VOH_MAX = VCC_MAX – 0.935V

(VCC_MAX – VOH_MAX) = 0.935V

•

For logic low, VOUT = VOL_MAX = VCC_MAX – 1.67V

(VCC_MAX – VOL_MAX) = 1.67V

Pd_H is power dissipation when the output drives high.

Pd_L is the power dissipation when the output drives low.

Pd_H = [(VOH_MAX– (VCC_MAX – 2V))/RL] * (VCC_MAX – VOH_MAX) = [(2V – (VCC_MAX – VOH_MAX))/RL] * (VCC_MAX – VOH_MAX) =

[(2V – 0.935V)/50

Ω] * 0.935V = 19.92mW

Pd_L = [(VOL_MAX – (VCC_MAX – 2V))/RL] * (VCC_MAX – VOL_MAX) = [(2V – (VCC_MAX – VOL_MAX))/RL] * (VCC_MAX – VOL_MAX) =

[(2V – 1.67V)/50

Ω] * 1.67V = 11.02mW

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

OUT

CC - 2V

Ω

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