LT3571_15 Datasheet, PDF (1/16 Pages) Linear Technology – 75V DC/DC Converter for APD Bias

FEATURES
n _{High APD Voltage: Up to 70V}
n _{Integrated Schottky Diode}
n _{75V, 370mA Internal Switch}
n _{High Side Fixed Voltage Drop APD Current Monitor}
n _{Adjustable Frequency: 250kHz to 2MHz}
n _{Frequency Synchronization}
n _{Wide VIN Range: 2.7V to 20V}
n _{Constant-Voltage and Constant-Current Regulation}
n _{Programmable Current Limit Protection}
n _{Surface Mount Components}
n _{Low Shutdown Current <1μA}
n _{Internal Soft-Start}
n _{Internal Compensation}
n _{CTRL Pin Allows Output Adjustment with}
No Polarity Inversion
n _{3mm × 3mm 16-Lead QFN Package}
APPLICATIONS
n _{APD Bias}
n _{PIN Diode Bias}
n _{Optical Receivers and Modules}
n _{Fiber Optic Network Equipment}
LT3571
75V DC/DC Converter
for APD Bias
DESCRIPTION
The LT^®3571 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 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.
TYPICAL APPLICATION
45V Low Noise APD Bias Power Supply
10μH
V_IN
5V
OFF ON
1μF
V_IN
SHDN
SW
V_OUT
V_REF
CTRL
50V
LT3571 MONIN
R_T
20Ω
10nF _1M
SYNC
FB
12.1k
1MHz
GND MON
APD
49.9Ω
45V
20.5k
0.1μF
10nF ^10k
0.1μF
3571 TA01a
APD Bias Ripple
500μV/DIV
I_APD = 1mA
500ns/DIV
3571 TA01b
3571fa
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