85304-01 データシートの表示（PDF） - Integrated Device Technology

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85304-01

Low Skew, 1-to-5, Differential-to-3.3V LVPECL Fanout Buffer

Integrated Device Technology 

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

85304-01 Data Sheet

Q1

VOUT

RL

50Ω

VCC - 2V

Figure 4. LVPECL Driver Circuit and Termination

To calculate output power dissipated due to loading, use the following equations which assume a 50 load, and a termination voltage of VCC

– 2V.

• For logic high, VOUT = VOH_MAX = VCC_MAX – 1.0V

(VCC_MAX – VOH_MAX) = 1.0V

• For logic low, VOUT = VOL_MAX = VCC_MAX – 1.7V

(VCC_MAX – VOL_MAX) = 1.7V

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 – 1.0V)/50] * 1.0V = 20mW

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

[(2V – 1.7V)/50] * 1.7V = 10.2mW

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

©2015 Integrated Device Technology, Inc

11

Revision E December 2, 2015

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