
ICS843156AK REVISION B NOVEMBER 28, 2012
15
2012 Integrated Device Technology, Inc.
ICS843156 Data Sheet
CRYSTAL-TO-LVPECL CLOCK SYNTHESIZER
3. Calculations and Equations.
The purpose of this section is to calculate the power dissipation for the LVPECL output pairs.
The LVPECL output driver circuit and termination are shown in Figure 7.
Figure 7. LVPECL Driver Circuit and Termination
To calculate power dissipation per output pair due to loading, use the following equations which assume a 50 load, and a termination voltage
of VCCO – 2V.
For logic high, VOUT = VOH_MAX = VCCO_MAX – 0.9V
(VCCO_MAX – VOH_MAX) = 0.9V
For logic low, VOUT = VOL_MAX = VCCO_MAX – 1.7V
(VCCO_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 – (VCCO_MAX – 2V))/RL] * (VCCO_MAX – VOH_MAX) = [(2V – (VCCO_MAX – VOH_MAX))/RL] * (VCCO_MAX – VOH_MAX) =
[(2V – 0.9V)/50
] * 0.9V = 19.8mW
Pd_L = [(VOL_MAX – (VCCO_MAX – 2V))/RL] * (VCCO_MAX – VOL_MAX) = [(2V – (VCCO_MAX – VOL_MAX))/RL] * (VCCO_MAX – VOL_MAX) =
[(2V – 1.7V)/50
] * 1.7V = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW
V
OUT
V
CC
V
CC - 2V
Q1
RL
50
Ω