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 optical power. The VSC7940 is available in die form or in a 32-pin TQFP package.
   
Features
• Power Supply: 5V ±5%
• 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
   
Applications
• SONET/SDH at 622Mb/s, 1.244Gb/s,
    2.488Gb/s, 3.125Gb/s
• Full-Speed Fibre Channel (1.062Gb/s)