ICS8S89831I Datasheet, PDF (16/21 Pages) Integrated Device Technology – Output frequency

ICS8S89831I Data Sheet
DIFFERENTIAL LVPECL-TO-LVPECL/ECL FANOUT BUFFER
3. Calculations and Equations.
The purpose of this section is to calculate the power dissipation for the LVPECL output pairs.
The LVPECL output driver circuit and termination are shown in Figure 8.
V_CC
Q1
V_OUT
RL
50Ω
V_CC - 2V
Figure 8. 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_CC – 2V.
• For logic high, V_OUT = V_{OH_MAX} = V_{CC_MAX} – 0.85V
(V_{CC_MAX} – V_{OH_MAX}) = 0.85V
• For logic low, V_OUT = V_{OL_MAX} = V_{CC_MAX} – 1.575V
(V_{CC_MAX} – V_{OL_MAX}) = 1.575V
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 – 0.85V)/50Ω] * 0.85V = 19.55mW
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 – 1.575V)/50Ω] * 1.575V = 13.39mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 32.94mW
ICS8S89831AKI REVISION A APRIL 26, 2010
16
©2010 Integrated Device Technology, Inc.