VITESSE
SEMICONDUCTOR CORPORATION
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Table 5: Pin Identifications
Pin Name
GND
V
CC
DATA+
DATA-
CLK+
CLK-
LATCH
ENABLE
DISABLE
BIASMON
MODMON
FAIL
APCFILT
BIAS
OUT+
OUT-
MD
CAPC
RESERVED
APCSET
MODSET
BIASMAX
Preliminary Data Sheet
VSC7939
Description
Pin Number
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 V
CC
if LATCH function is not used.
Negative Clock Input (PECL). Leave unconnected if LATCH function is not used.
Latch Input (TTL/CMOS). Connect to V
CC
for data retiming and GND for direct data.
Enable Input (TTL/CMOS). If used, connect DISABLE to GND. Connect to V
CC
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 V
CC
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. I
MOD
flows when input data is high.
Negative Modulation-Current Output. I
MOD
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
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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
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
