853006AG www.icst.com/products/hiperclocks.html REV. A NOVEMBER 9, 2004
13
Integrated
Circuit
Systems, Inc.
ICS853006
LOW SKEW, 1-TO-6
DIFFERENTIAL-TO-2.5V/3.3V LVPECL/ECL FANOUT BUFFER
3. Calculations and Equations.
LVPECL output driver circuit and termination are shown in
Figure 6.
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
– 0.935V
(V
CC_MAX
- V
OH_MAX
)
= 0.935V
• For logic low, V
OUT
= V
OL_MAX
= V
CC_MAX
– 1.67V
(V
CC_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
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 - 0.935V)/50Ω] * 0.935V = 19.92mW
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 - 1.67V)/50Ω] * 1.67V = 11.02mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30.94mW
FIGURE 6. LVPECL DRIVER CIRCUIT AND TERMINATION
VOUT
Q1
VCC - 2V
RL
50
VCC
