ICS853S310I Datasheet, PDF (14/17 Pages) Integrated Device Technology – Two selectable differential input pairs

ICS853S310I Data Sheet
LOW SKEW, 1-TO-8 DIFFERENTIAL-TO-3.3V LVPECL/ECL FANOUT BUFFER
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 6.
V_CCO
Q1
V_OUT
RL
50Ω
V_CCO - 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
V_CCO – 2V.
• For logic high, V_OUT = V_{OH_MAX} = V_{CCO_MAX} – 0.89V
(V_{CCO_MAX} – V_{OH_MAX}) = 0.89V
• For logic low, V_OUT = V_{OL_MAX} = V_{CCO_MAX} – 1.67V
(V_{CCO_MAX} – V_{OL_MAX}) = 1.67V
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 – 0.89V)/50Ω] * 0.89V = 19.76mW
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 – 1.67V)/50Ω] * 1.67V = 11.02mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30.78mW
ICS853S310CVI REVISION A NOVEMBER 17, 2010
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