ICS853S12I Datasheet, PDF (13/17 Pages) Integrated Device Technology – Maximum output frequency

ICS853S12I
LOW SKEW, 1-TO-12, DIFFERENTIAL-TO-3.3V, 2.5V LVPECL 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 6.
V_CC
Q1
V_OUT
RL
50Ω
V_CC - 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 of V - 2V.
CC
• For logic high, V = V = V – 0.8V
OUT
OH_MAX
CC_MAX
(V - V ⁾ = 0.8V
CC_MAX
OH_MAX
• For logic low, V = V = V – 1.6V
OUT
OL_MAX
CC_MAX
(V - V ⁾ = 1.6V
CC_MAX
OL_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
L
CC_MAX
OH_MAX
CC_MAX
OH_MAX
L
CC_MAX
OH_MAX
[(2V - 0.8V)/50Ω] * 0.8V = 19.2mW
Pd_L = [(V – (V - 2V))/R ] * (V - V ) = [(2V - (V - V ^))/R ] * (V - V ) =
OL_MAX
CC_MAX
L
CC_MAX
OL_MAX
CC_MAX
OL_MAX
L
CC_MAX
OL_MAX
[(2V - 1.6V)/50Ω] * 1.6V = 12.8mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 32mW
IDT^™ / ICS^™ LVPECL FANOUT BUFFER
13
ICS853S12AKI REV. A MAY 21, 2008