ICS85311AM

www.icst.com/products/hiperclocks.html

REV. A JUNE 29, 2001

10

Integrated

Circuit

Systems, Inc.

ICS85311

Low Skew, 1-to-2

Differential-to-2.5V/3.3V ECL/LVPECL Fanout Buffer

3. Calculations and Equations.

LVPECL output driver circuit and termination are shown in Figure 9.

To calculate worst case power dissipation into the load, use the following equations which assume a 50Ω load,

and a termination voltage of V

CC

- 2V.

Pd_H is power dissipation when the output drives high.

Pd_L is the power dissipation when the output drives low.

Pd_H = [(V

OH_MAX

– (V

CC

- 2V))/R

L

]*(V

CC

- V

OH_MAX

)

Pd_L = [(V

OL_MAX

– (V

CC

- 2V))/R

L

]*(V

CC

- V

OL_MAX

)

•

For logic high , V

OUT

= V

OH_MAX

= V

CC

– 1.0V

Using V

CC

= 3.465, this results in V

OH_MAX

= 2.465V

•

For logic low , V

OUT

= V

OL_MAX

= V

CC

– 1.7V

Using V

CC

= 3.465, this results in V

OL_MAX

= 1.765V

Pd_H = [(2.465V - (3.465V - 2V))/50 Ω]*(3.465V - 2.465V) = 20.0mW

Pd_L = [(1.765V - (3.465V - 2V))/50 Ω]*(3.465V - 1.765V) = 10.2mW

Total Power Dissipation per output pair = Pd_H + Pd_L = 30.2mW

Q1

V

OUT

V

CC

RL

50

V

Figure 9 - LVPECL Driver Circuit and Termination