ICS85311 Datasheet, PDF (10/13 Pages) Integrated Circuit Systems – Low Skew, 1-to-2 Differential-to-2.5V/3.3V ECL/LVPECL Fanout Buffer

Integrated
Circuit
Systems, Inc.
ICS85311
Low Skew, 1-to-2
Differential-to-2.5V/3.3V ECL/LVPECL Fanout Buffer
3. Calculations and Equations.
LVPECL output driver circuit and termination are shown in Figure 9.
V_CC
Q1
V
OUT
RL
50
V_CC - 2V
Figure 9 - 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 - 2V.
CC
Pd_H is power dissipation when the output drives high.
Pd_L is the power dissipation when the output drives low.
Pd_H = [(V
– (V - 2V))/R ]*(V - V
)
OH_MAX
CC
L
CC OH_MAX
Pd_L = [(V
– (V - 2V))/R ]*(V - V
)
OL_MAX
CC
L
CC OL_MAX
• For logic high , V = V
= V – 1.0V
OUT
OH_MAX
CC
Using V = 3.465, this results in V
= 2.465V
CC
OH_MAX
• For logic low , V = V
= V – 1.7V
OUT
OL_MAX
CC
Using V = 3.465, this results in V
= 1.765V
CC
OL_MAX
Pd_H = [(2.465V - (3.465V - 2V))/50 Ω]*(3.465V - 2.465V) = 20.0mW
Pd_L = [(1.765V - (3.465V - 2V))/50 Ω]*(3.465V - 1.765V) = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30.2mW
ICS85311AM
www.icst.com/products/hiperclocks.html
10
REV. A JUNE 29, 2001