Communications Power

Boost DC-DC with Avalanche Photodiode Current Monitor

The LT3905 is a fixed-frequency, current-mode step-up dc-dc converter from Linear Technology Corp. designed to bias avalanche photodiodes (APD) in optical receivers. The LT3905 features high-side APD current monitoring with over five decades of dynamic range and better than 2% relative accuracy over the 3µA to 3mA range. The maximum APD current is programmed with a single resistor and a fast current limiter with indicator protects the APD during overload conditions. Adjustable output voltage provides dynamic bias control and a programmable loss-of-signal indicator flags low APD current. The power switch, Schottky diode, APD current monitor, current limit and loss-of-signal indicator are integrated into a single IC that is packaged in a 3mm x 3mm QFN. Operating at 1MHz or 2MHz switching frequency, the LT3905 offers a tiny solution footprint for APD biasing applications.

The LT3905's internal 65V, 350mA high efficiency switch offers output voltages as high as 60V while its 2.7V to 12V input voltage range accommodates a wide range of input sources. Its switching frequency is user selectable at 1MHz or 2MHz, enabling the designer to optimize efficiency while minimizing the size of the external components. Constant frequency architecture is used to minimize output noise. Other features include soft-start, internal compensation and programmable VIN undervoltage lockout.

The LT3905EUD is available in a 3mm x 3mm QFN-16 and is priced starting at $2.55 each in 1,000-piece quantities. An industrial grade version, the LT3905IUD, is tested and guaranteed to operate from a -40°C to 125°C operating junction temperature and is priced starting at $2.81 each in 1,000-piece quantities.

Linear Technology Corporation
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