ICS84330CI Datasheet, PDF (14/20 Pages) Integrated Circuit Systems – 720MHZ, LOW JITTER, CRYSTAL-TO-3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER

ICS84330CI Data Sheet
720MHZ, CRYSTAL-TO-LVPECL FREQUENCY SYNTHESIZER
3. Calculations and Equations.
The purpose of this section is to calculate the power dissipation for the LVPECL output pair.
LVPECL output driver circuit and termination are shown in Figure 7.
V_CC
Q1
V_OUT
RL
50Ω
V_CC - 2V
Figure 7. LVPECL Driver Circuit and Termination
To calculate worst case power dissipation into the load, use the following equations which assume a 50 load, and a termination voltage of
V_CC - 2V.
• For logic high, V_OUT = V_{OH_MAX} = V_{CC_MAX} - 0.9V
(V_{CC_MAX} - V_{OH_MAX}) = 0.9V
• For logic low, V_OUT = V_{OL_MAX} = V_{CC_MAX} - 1.7V
(V_{CC_MAX} - V_{OL_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 = [(V_{OH_MAX} - (V_{CC_MAX} -2V))/R_L] * (V_{CC_MAX} - V_{OH_MAX}) = [(2V - (V_{CC_MAX} - V_{OH_MAX}))/R_L] * (V_{CC_MAX} - V_{OH_MAX}) =
[(2V - 0.9V)/50] * 0.9V = 19.8mW
Pd_L = [(V_{OL_MAX} - (V_{CC_MAX} -2V))/R_L] * (V_{CC_MAX} - V_{OL_MAX}) = [(2V - (V_{CC_MAX} - V_{OL_MAX}))/R_L] * (V_{CC_MAX} - V_{OL_MAX}) =
[(2V - 1.7V)/50] * 1.7V = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW
ICS84330CVI REVISION A JANUARY 7, 2011
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©2011 Integrated Device Technology, Inc.