75V DC/DC Converter for APD Bias

The LT3571 is a current mode step-up DC/DC converter designed to bias avalanche photodiodes (APDs) in optical receivers with an output voltage up to 75V. The LT3571 features a high side fixed voltage drop APD current monitor with better than 10% relative accuracy over the entire temperature range. The integrated power switch, Schottky diode and APD current monitor allow a small solution footprint and low solution cost. It combines a traditional voltage loop and a unique current loop to operate as a constant-current source or constant-voltage source. The inductor-based topology ensures an input free from switching noise. The integrated high side current monitor produces a current proportional to the APD current with better than 10% relative accuracy over four decades of dynamic range in the input range of 250nA to 2.5mA. This current can be used as a reference to provide a digitally programmed output voltage via the CTRL pin. The LT3571 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

* High Output Voltage: Up to 75V

* Integrated Schottky Diode

* 75V, 350mA Internal Switch

* High Side Fixed Voltage Drop APD Current Monitor

* Adjustable Frequency: 250kHz to 2MHz

* Frequency Synchronization

* Wide VIN Range: 2.7V to 20V

* Constant-Voltage and Constant-Current Regulation

* Programmable Current Limit Protection

* Surface Mount Components

* Low Shutdown Current <1μA

* Internal Soft-Start

* Internal Compensation

* CTRL Pin Allows Output Adjustment with No Polarity Inversion

* 3mm × 3mm 16-Lead QFN Package