ICS87993I Datasheet, PDF (12/16 Pages) Integrated Circuit Systems – 1-TO-5 DIFFERENTIAL-TO-3.3V LVPECL PLL CLOCK DRIVER W/DYNAMIC CLOCK SWITCH

Integrated
Circuit
Systems, Inc.
ICS87993I
1-TO-5 DIFFERENTIAL-TO-3.3V LVPECL
PLL CLOCK DRIVER W/DYNAMIC CLOCK SWITCH
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
50
V - 2V
CC
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
– 1.0V
OUT
OH_MAX
CC_MAX
(V
- V ⁾ = 1.0V
CC_MAX OH_MAX
• For logic low, V = V = V – 1.7V
OUT
OL_MAX
CC_MAX
(V
- V ⁾ = 1.7V
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 - 1V)/50Ω] * 1V = 20.0mW
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 - 1.7V)/50Ω] * 1.7V = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30.2mW
87993AYI
www.icst.com/products/hiperclocks.html
12
REV. B May 21, 2003