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VSC7939W

SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control

Vitesse Semiconductor 

VITESSE

SEMICONDUCTOR CORPORATION

SONET/SDH 3.125Gb/s

Laser Diode Driver with Automatic Power Control

Preliminary Data Sheet

VSC7939

Table 5: Pin Identifications

Pin Name Pin Number

Description

GND

VCC

DATA+

DATA-

CLK+

CLK-

LATCH

ENABLE

DISABLE

BIASMON

MODMON

FAIL

APCFILT

BIAS

OUT+

OUT-

MD

CAPC

RESERVED

APCSET

MODSET

BIASMAX

15, 22, 23, 27

1, 4, 7, 16,

18, 21, 25, 32

2

3

5

6

8

9

10

11

12

13

14

17

19

20

24

26

28

29

30

31

Ground

Power Supply

Positive Data Input (PECL)

Negative Data Input (PECL)

Positive Clock Input (PECL). Connect to VCC if LATCH function is not used.

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

Latch Input (TTL/CMOS). Connect to VCC for data retiming and GND for direct data.

Enable Input (TTL/CMOS). If used, connect DISABLE to GND. Connect to VCC for

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

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

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

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

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

modulation current.

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

No effect on device operation..

Laser Bias Current Output

Positive Modulation-Current Output. IMOD flows when input data is high.

Negative Modulation-Current Output. IMOD flows when input data is low.

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

filter high-speed AC monitor photocurrent.

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

Do not connect.

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

resistor to GND.

Connect resistor to GND to set desired modulation current.

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

this value, but cannot add to it.

Page 8

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

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

Internet: www.vitesse.com

G52350-0, Rev 3.2

02/26/01

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