ICS843021I-01 Datasheet, PDF (11/14 Pages) Integrated Circuit Systems – FEMTOCLOCKS-TM CRYSTAL-TO-3.3V, 2.5V 125MHZ LVPECL CLOCK GENERATOR

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS843021I-01
FEMTOCLOCKS™ CRYSTAL-TO-3.3V, 2.5V
125MHZ LVPECL CLOCK GENERATOR
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 5.
V_CC
Q1
V_OUT
RL
50
V_CC - 2V
FIGURE 5. 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
– 0.9V
OUT
OH_MAX
CC_MAX
(V
- V ⁾ = 0.9V
CCO_MAX OH_MAX
• For logic low, V = V = V – 1.7V
OUT
OL_MAX
CC_MAX
(V
- V ⁾ = 1.7V
CCO_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 - 0.9V)/50Ω] * 0.9V = 19.8mW
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 = 30mW
843021AGI-01
www.icst.com/products/hiperclocks.html
11
REV. A NOVEMBER 30, 2004