Boost DC/DC Converter with APD Current Monitor

The LT3905 is a fixed frequency current-mode step-up converter designed to bias avalanche photodiodes (APD) in optical receivers. The LT3905 features high side APD current monitoring over four decades of dynamic range with 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 an adjustable loss-of-signal indicator flags low APD current.

Coupled with the integrated DMOS power switch and Schottky rectifier, the LT3905 provides a compact total solution with few external components and low solution cost. Constant switching frequency results in predictable output noise that is easy to filter.

The LT3905 is available in the tiny footprint (3mm × 3mm) 16-Lead QFN Package.

Applications

* APD Bias

* PIN Diode Bias

* Optical Receivers and Modules

* Fiber Optic Network Equipment

* 65V, 350mA Internal DMOS Switch* Integrated Schottky Diode* 2% Accurate APD Current Monitoring Over the 3μA to 3mA Range* Single Resistor Programs Maximum APD Current* Fast APD Current Limiter with Indicator* Programmable Loss-of-Signal Indicator* CTRL Pin Adjusts Output Voltage* Programmable VIN Undervoltage Lockout* High Efficiency Step-Up Converter* Selectable 1MHz/2MHz Switching Frequency* Internally Compensated* Internal Soft-Start* 2.7V to 12V VIN Range* Low Shutdown Current: <1μA