ICS85301
2:1
DIFFERENTIAL-TO-LVPECL MULTIPLEXER
Integrated
Circuit
Systems, Inc.
3. Calculations and Equations.
The purpose of this section is to derive the power dissipated into the load.
LVPECL output driver circuit and termination are shown in Figure 6.
VCC
Q1
VOUT
RL
50
VCC - 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 ofV - 2V.
CC
•
•
For logic high, VOUT = V
= V
– 1.005V
CC_MAX
OH_MAX
)
= 1.005
OH_MAX
(V
- V
CC_MAX
For logic low, VOUT = V
= V
– 1.78V
OL_MAX
CC_MAX
)
= 1.78V
OL_MAX
(V
- V
CC_MAX
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
) = [(2V - (V
- V
/R ] * (V
- V
) =
OH_MAX
CC_MAX
CC_MAX
OH_MAX
CC_MAX
OH_MAX
CC_MAX
OH_MAX
L
L
[(2V - 1.005V)/50Ω] * 1.005V = 20mW
))
Pd_L = [(V
– (V
- 2V))/R ] * (V
- V
) = [(2V - (V
- V
/R ] * (V
- V
) =
OL_MAX
CC_MAX
CC_MAX
OL_MAX
CC_MAX
OL_MAX
CC_MAX
OL_MAX
L
L
[(2V - 1.78V)/50Ω] * 1.78V = 7.83mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 27.83mW
85301AK
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REV.A JANUARY 16, 2006
14
ICSI [ INTEGRATED CIRCUIT SOLUTION INC ]
