VSC7938 Datasheet, PDF (1/16 Pages) Vitesse Semiconductor Corporation – Laser Diode Driver with Automatic Power Control

VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7938
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Features
• Power Supply: 3.3V or 5V ±5%
• AC-Coupled to Laser Diode
• Programmable Modulation Current: 5mA to 60mA
• Programmable Bias Current: 1mA to 100mA
• Enable/Disable Control
• Typical Rise/Fall Times of 60ps
• Automatic Optical Average Power Control
• Supply Current of 33mA at 3.3V
Applications
• SDH/SONET at 622Mb/s, 1.244Gb/s,
2.488Gb/s, 3.125Gb/s
• Full-Speed Fibre Channel (1.062Gb/s)
General Description
The VSC7938 is a single 3.3V or 5V supply laser diode driver specially designed for SDH/SONET applica-
tions 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 con-
trolled with an external capacitor. Other features include enable/disable control, short-circuit protection for the
modulation and bias inputs, short rise and fall times, 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 optical power. The
VSC7938 is available in die form or in a 48-pin TQFP package.
Block Diagram
3.3V Operation
V_CC
LATCH
DATA+
DATA-
CLK+
CLK-
MUX
SET
DQ
CLR ^Q
IOUT+
C_D
IOUT-
C_F
R_F
V_CC
BIAS
ENABLE
DISABLE
APC
MD
FAIL
1nF
SLWSTRT MODSET BIASMAX CAPC APCSET
G52349-0, Rev 3.0
01/20/01
© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: [phone] • Email: [e-mail]
Internet: www.vitesse.com
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