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 7

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

Table 5: Pin Identifications

Pin Name

Pin Number

Description

GND

10, 15, 22,

23, 27

Ground

1, 4, 7, 16, 18,

21, 25, 32

Power Supply

DATA+

2

Positive Data Input (PECL)

DATA-

3

Negative Data Input (PECL)

CLK+

5

CLK-

6

Negative Clock Input (PECL). Leave unconnected if LATCH function is not used.

LATCH

8

ENABLE

9

normal operation and GND to disable laser bias and modulation currents.

DISABLE

10

Disable Input (TTL/CMOS). If used, leave ENABLE pin floating. Connect to GND for

BIASMON

11

Bias Current Monitor. Sink current source that is proportional to the laser bias current.

MODMON

12

Modulation Current Monitor. Sink current source that is proportional to the laser

modulation current.

FAIL

13

Output (TTL/CMOS). When low, indicates APC failure.

APCFILT

14

No effect on device operation.

BIAS

17

Laser Bias Current Output

OUT+

19

OUT-

20

MD

24

Monitor Diode Input. Connect to monitor photodiode anode. Connect capacitor to GND to

filter high-speed AC monitor photocurrent.

CAPC

26

Capacitor to GND sets dominant pole of the APC feedback loop.

RESERVED

28

Do not connect.

APCSET

29

Resistor to GND sets desired average optical power. If APC is not used, connect 100k

Ω

resistor to GND.

MODSET

30

Connect resistor to GND to set desired modulation current.

BIASMAX

31

Connect resistor to GND to set maximum bias current. The APC function can subtract from

this value, but cannot add to it.