The MAX3668 is a complete, +3.3V laser driver with automatic power control (APC) circuitry for SDH/SONET applications up to 622Mbps. It accepts differential PECL inputs, provides bias and modulation currents, and operates over a temperature range of -40°C to +85°C. An APC feedback loop is incorporated to maintain a constant average optical power over temperature and lifetime. The wide modulation current range of 5mA to 75mA and bias current of 1mA to 80mA are easy to program, making this product ideal for use in various SDH/SONET applications. The MAX3668 also provides enable control and a failure-monitor output to indicate when the APC loop is unable to maintain the average optical power. The MAX3668 is available in a 5mm 32-pin TQFP package as well as in dice.
The MAX3668 is a 3.3 V laser driver designed for SDH/SONET applications up to 622 Mbps. It accepts differential PECL inputs, provides programmable bias (1‑80 mA) and modulation (5‑75 mA) currents, and includes an automatic power control (APC) loop to keep average optical power constant over temperature and lifetime.
The device is supplied in a 32‑pin TQFP package (5 mm × 5 mm) and offers enable control, a failure‑monitor output, and short‑circuit protection. Detailed electrical characteristics, pin descriptions, and design guidelines are provided for system integration.
| Supply Current | 38 mA |
|---|---|
| Bias Current Range | 1 mA – 80 mA |
| Modulation Current Range | 5 mA – 75 mA |
| Rise/Fall Time | <200 ps |
| Supply Voltage Operation | Single +3.3 V or +5.0 V |
| Enable Control Timing | 250 ns typical enable time |
| APC Failure Monitor | FAIL pin goes low on APC loop failure |
The typical supply current is 38 mA.
Pull the ENABLE pin low; both bias and modulation currents are turned off.
FAIL goes low when the APC loop cannot maintain the desired average optical power.
The device can deliver up to 75 mA of modulation current.