Features

• 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 V_IN 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

Typical Application

Description

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.