ICS849N202I Datasheet, PDF (33/39 Pages) Integrated Device Technology – FemtoClock® NG Universal Frequency Translator

ICS849N202I Data Sheet
FemtoClock® NG Universal Frequency Translator
3. Calculations and Equations.
The purpose of this section is to calculate the power dissipation for the LVPECL output pairs.
LVPECL output driver circuit and termination are shown in Figure 12.
V_CCO
Q1
V_OUT
RL
50Ω
V_CCO - 2V
Figure 12. 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} – 0.7V
(V_{CCO_MAX} – V_{OH_MAX}) = 0.7V
• For logic low, V_OUT = V_{OL_MAX} = V_{CCO_MAX} – 1.5V
(V_{CCO_MAX} – V_{OL_MAX}) = 1.5V
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 – 0.7V)/50Ω] * 0.7V = 18.2mW
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 – 1.5V)/50Ω] * 1.5V = 15mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 33.2mW
ICS849N202CKI REVISION A SEPTEMBER 26, 2011
33
©2011 Integrated Device Technology, Inc.