LT3571

1

3571fa

TYPICAL APPLICATION

DESCRIPTION

75V DC/DC Converter

for APD Bias

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 moni-

tor 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.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

45V Low Noise APD Bias Power Supply

FEATURES

APPLICATIONS

No Polarity Inversion

× 3mm 16-Lead QFN Package

APD Bias Ripple

1μF

MONIN

SHDN

CTRL

GND

SYNC

FB

SW

LT3571

MON

APD

OFF ON

5V

20.5k

49.9Ω

45V

12.1k

1MHz

3571 TA01a

0.1μF

10k

10nF

50V

0.1μF

10μH

1M

20Ω

10nF

500ns/DIV

3571 TA01b

500μV/DIV