LT3571
75V DC/DC Converter
for APD Bias
FEATURES DESCRIPTION
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High APD Voltage: Up to 70V The LT 3571 is a current mode step-up DC/DC converter
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Integrated Schottky Diode designed to bias avalanche photodiodes (APDs) in optical
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75V, 370mA Internal Switch receivers with an output voltage up to 75V. The LT3571
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High Side Fixed Voltage Drop APD Current Monitor features a high side xed voltage drop APD current moni-
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Adjustable Frequency: 250kHz to 2MHz tor with better than 10% relative accuracy over the entire
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Frequency Synchronization temperature range. The integrated power switch, Schottky
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Wide V Range: 2.7V to 20V diode and APD current monitor allow a small solution
IN
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Constant-Voltage and Constant-Current Regulation footprint and low solution cost. It combines a traditional
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Programmable Current Limit Protection voltage loop and a unique current loop to operate as
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Surface Mount Components a constant-current source or constant-voltage source.
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Low Shutdown Current <1A The inductor-based topology ensures an input free from
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Internal Soft-Start switching noise. The integrated high side current monitor
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Internal Compensation produces a current proportional to the APD current with
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CTRL Pin Allows Output Adjustment with better than 10% relative accuracy over four decades of
No Polarity Inversion dynamic range in the input range of 250nA to 2.5mA. This
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3mm 3mm 16-Lead QFN Package 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
APPLICATIONS
QFN package.
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APD Bias
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
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Technology Corporation. All other trademarks are the property of their respective owners.
PIN Diode Bias
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Optical Receivers and Modules
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Fiber Optic Network Equipment
TYPICAL APPLICATION
45V Low Noise APD Bias Power Supply APD Bias Ripple
10H
V
IN
5V
V SW
IN
V
OFF ON SHDN OUT
20
V
1F REF
50V 500V/DIV
CTRL LT3571 MONIN
10nF
R
1M
T
SYNC
FB
GND MON APD
20.5k 3571 TA01b
I = 1mA 500ns/DIV
APD
12.1k
49.9
0.1F
1MHz
45V
10k
10nF 0.1F
3571 TA01a
3571fa
1LT3571
ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION
(Note 1)
TOP VIEW
Input Voltage (V ), SHDN ........................................20V
IN
V , MONIN, APD ....................................................75V
OUT
16 15 14 13
MON .......................................................................... 12V
NC 1 12 SHDN
SW ............................................................................75V
APD 2 11 V
IN
17
CTRL, FB, SYNC ..........................................................5V
MONIN 3 10 GND
R , V ................................................................... 1.5V
V 4 9 R
T REF
OUT T
5 6 7 8
Operating Ambient Temperature Range
(Note 2) .............................................40C to 125C
Operating Junction Temperature
UD PACKAGE
16-LEAD (3mm s 3mm) PLASTIC QFN
(Note 2) .............................................40C to 125C
T = 125C, = 68C/W, = 4.2C/W (NOTE 2)
JMAX JA JC
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
Storage Temperature Range ...................65C to 150C
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3571EUD#PBF LT3571EUD#TRPBF LDTN 40C to 125C
16-Lead (3mm 3mm) Plastic QFN
LT3571IUD#PBF LT3571IUD#TRPBF LDTN 16-Lead (3mm 3mm) Plastic QFN 40C to 125C
Consult LTC Marketing for parts speci ed with wider operating temperature ranges. *The temperature grade is identi ed by a label on the shipping container.
For more information on lead free part marking, go to: