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ICS843SDN Datasheet, PDF (11/14 Pages) Integrated Device Technology – FEMTOCLOCK™ CRYSTAL-TO-3.3V LVPECL CLOCK GENERATOR
ICS843SDN
FEMTOCLOCK™CRYSTAL-TO-3.3V LVPECL CLOCK GENERATOR
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 6.
VCC
Q1
VOUT
RL
50Ω
VCC - 2V
Figure 6. 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 – 0.9V
(VCC_MAX – VOH_MAX) = 0.9V
• 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 – 0.9V)/50Ω] * 0.9V = 19.8mW
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)/50Ω] * 1.7V = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW
IDT™ / ICS™ 3.3V LVPECL CLOCK GENERATOR
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ICS843SDNAG REV. A FEBRUARY 19, 2009