ICS8430002 Datasheet, PDF (22/27 Pages) Integrated Device Technology – High-Performance Fractional-N Frequency Synthesizer

ICS8430002 Data Sheet
HIGH-PERFORMANCE FRACTIONAL-N 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 10.
V_CCO
Q1
V_OUT
RL
50Ω
V_CCO - 2V
Figure 10. 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
V_CCO – 2V.
• For logic high, V_OUT = V_{OH_MAX} = V_{CCO_MAX} – 0.9V
(V_{CCO_MAX} – V_{OH_MAX}) = 0.9V
• For logic low, V_OUT = V_{OL_MAX} = V_{CCO_MAX} – 1.7V
(V_{CCO_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_{CCO_MAX} – 2V))/R_L] * (V_{CCO_MAX} – V_{OH_MAX}) = [(2V – (V_{CCO_MAX} – V_{OH_MAX}))/R_L] * (V_{CCO_MAX} – V_{OH_MAX}) =
[(2V – 0.9V)/50Ω] * 0.9V = 19.8mW
Pd_L = [(V_{OL_MAX} – (V_{CCO_MAX} – 2V))/R_L] * (V_{CCO_MAX} – V_{OL_MAX}) = [(2V – (V_{CCO_MAX} – V_{OL_MAX}))/R_L] * (V_{CCO_MAX} – V_{OL_MAX}) =
[(2V – 1.7V)/50Ω] * 1.7V = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW
ICS8430002AY REVISION C NOVEMBER 12, 2009
22
©2009 Integrated Device Technology, Inc.