VITESSE

SEMICONDUCTOR CORPORATION

Preliminary Data Sheet

VSC7940

SONET/SDH 3.125Gb/s

Laser Diode Driver with Automatic Power Control

G52357-0, Rev 3.2

Page 1

05/11/01

© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012

Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com

Internet: www.vitesse.com

Features

Applications

General Description

The VSC7940 is a single 5V supply laser diode driver specially designed for SONET/SDH applications up

to 3.125Gb/s. External resistors set a wide range of bias and modulation currents for driving the laser. Data and

clock inputs accept differential PECL signals. The Automatic Power Control (APC) loop maintains a constant

average optical power over temperature and lifetime. The dominant pole of the APC loop can be controlled with

an external capacitor. Other features include enable/disable control, programmable slow-start circuit to set laser

turn-on delay, and failure-monitor output to indicate when the APC loop is unable to maintain the average opti-

cal power. The VSC7940 is available in die form or in a 32-pin TQFP package.

Block Diagram

• Power Supply: 5V

• DC-Coupled to Laser Diode

• Programmable Modulation Current: 5mA to 100mA

• Programmable Bias Current: 1mA to 100mA

• Enable/Disable Control

• Automatic Optical Average Power Control

• Modulation and Bias Current Monitors

Q

SET

CLR

Q

D

MUX

MODSET

BIASMAX

CAPC

APC

APCSET

LATCH

1nF

MODMON

MD

FAIL

BIAS

BIASMON

DATA+

DATA-

CLK+

CLK-

ENABLE

DISABLE

V

CC

V

CC

V

CC

IOUT+

IOUT-

V

CC

R

F

C

F

• SONET/SDH at 622Mb/s, 1.244Gb/s,

2.488Gb/s, 3.125Gb/s

• Full-Speed Fibre Channel (1.062Gb/s)