ICS873990 Datasheet, PDF (12/16 Pages) Integrated Circuit Systems – LOW VOLTAGE, LVCMOS/ CRYSTAL-TO-LVPECL/ECL CLOCK GENERATOR

Integrated
Circuit
Systems, Inc.
ICS873990
LOW VOLTAGE, LVCMOS/
CRYSTAL-TO-LVPECL/ECL 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
CCO
Q1
V
OUT
RL
50
V - 2V
CCO
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.
CCO
• For logic high, V = V
=V
– 0.9V
OUT
OH_MAX
CCO_MAX
(V
- V ⁾ = 0.9V
CCO_MAX OH_MAX
• For logic low, V = V = V
– 1.7V
OUT
OL_MAX
CCO_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
CCO_MAX
L
CCO_MAX OH_MAX
CCO_MAX OH_MAX
L
CCO_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
CCO_MAX
L
CCO_MAX OL_MAX
CCO_MAX OL_MAX
L
CCO_MAX OL_MAX
[(2V - 1.7V)/50Ω] * 1.7V = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW
873990AY
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12
REV. B JUNE 13, 2005