85357AG-01

www.icst.com/products/hiperclocks.html

REV. A JULY 16, 2001

9

Integrated

Circuit

Systems, Inc.

ICS85357-01

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 8.

Ω 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_MAX

- 2V))/R

L

] * (V

CC_MAX

- V

OH_MAX

)

Pd_L = [(V

OL_MAX

– (V

CC_MAX

- 2V))/R

L

] * (V

CC_MAX

- V

OL_MAX

)

•

For logic high, V

OUT

= V

OH_MAX

= V

CC_MAX

– 1.0V

Using V

CC_MAX

= 3.465, this results in V

OH_MAX

= 2.465V

•

For logic low, V

OUT

= V

OL_MAX

= V

CC_MAX

– 1.7V

Using V

CC_MAX

= 3.465, this results in V

OL_MAX

= 1.765V

Pd_H = [(2.465V - (3.465V - 2V))/50

Ω] * (3.465V - 2.465V) = 20mW

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 8 - LVPECL Driver Circuit and Termination