IDT
™
/ ICS
™
1-TO-9, 2.5V, 3.3V LVPECL/ECL FANOUT BUFFER 16 ICS853031AY REV. C AUGUST 12, 2008
ICS853031
LOW SKEW, 1-TO-9, DIFFERENTIAL-TO-2.5, 3.3V LVPECL/ECL FANOUT BUFFER
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 8.
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
– 0.935V
(V
CCO_MAX
– V
OH_MAX
)
= 0.935V
• 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 – 0.935V)/50Ω] * 0.935V = 19.92mW
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 = 11.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30.94mW
FIGURE 8. LVPECL DRIVER CIRCUIT AND TERMINATION
VCCO - 2V
Q1
VOUT
RL
50
VCCO
