ICS8535-11 Datasheet, PDF (11/14 Pages) Integrated Circuit Systems – LOW SKEW, 1-TO-4, CRYSTAL OSCILLATOR/ LVCMOS-TO-3.3V LVPECL FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
ICS8535-11
LOW SKEW, 1-TO-4, CRYSTAL OSCILLATOR/
LVCMOS-TO-3.3V 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 10.
V_CC
Q1
V_OUT
RL
50
V_CC - 2V
FIGURE 10 - 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
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 )
OH_MAX
CC_MAX
L
CC_MAX OH_MAX
Pd_L = [(V – (V - 2V))/R ] * (V - V )
OL_MAX
CC_MAX
L
CC_MAX OL_MAX
• For logic high, V = V
=V
– 1.0V
OUT
OH_MAX
CC_MAX
Using V
= 3.465, this results in V
= 2.465V
CC_MAX
OH_MAX
• For logic low, V = V = V – 1.7V
OUT
OL_MAX
CC_MAX
Using V = 3.465, this results in V = 1.765V
CC_MAX
OL_MAX
Pd_H = [(2.465V - (3.465V - 2V))/50Ω] * (3.465V - 2.465V) = 20mW
Pd_L = [(1.765V - (3.465V - 2V))/50Ω] * (3.465V - 1.765V) = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30.2mW
8535AG-11
www.icst.com/products/hiperclocks.html
11
REV. B JULY 27, 2001