LT3905
Boost DC/DC Converter
with APD Current Monitor
Fea T Descrip T
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65V, 350mA Internal DMOS Switch The LT 3905 is a fixed frequency current-mode step-up
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Integrated Schottky Diode converter designed to bias avalanche photodiodes (APD)
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2% Accurate APD Current Monitoring Over the 3A in optical receivers. The LT3905 features high side APD
to 3mA Range current monitoring over four decades of dynamic range
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Single Resistor Programs Maximum APD Current with better than 2% relative accuracy over the 3A to
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Fast APD Current Limiter with Indicator 3mA range.
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Programmable Loss-of-Signal Indicator
The maximum APD current is programmed with a single
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CTRL Pin Adjusts Output Voltage
resistor, and a fast current limiter with indicator protects
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Programmable V Undervoltage Lockout
IN
the APD during overload conditions. Adjustable output
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High Efficiency Step-Up Converter
voltage provides dynamic bias control, and an adjustable
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Selectable 1MHz/2MHz Switching Frequency
loss-of-signal indicator flags low APD current.
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Internally Compensated
n Coupled with the integrated DMOS power switch and
Internal Soft-Start
n Schottky rectifier, the LT3905 provides a compact total
2.7V to 12V V Range
IN
n solution with few external components and low solution
Low Shutdown Current: <1A
cost. Constant switching frequency results in predictable
output noise that is easy to filter.
a T
The LT3905 is available in the tiny footprint (3mm 3mm)
n
APD Bias
16-Lead QFN Package.
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PIN Diode Bias
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
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Optical Receivers and Modules Technology Corporation. All other trademarks are the property of their respective owners.
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Fiber Optic Network Equipment
Typical a T
Adjustable APD Bias Supply
10H
Input Current vs APD Current
V
IN
2.7V to 12V
125
1F
UP TO 54V
V = 45V
APD
V SW
EN/UVLO IN V
OUT
LOS_ADJ
634k
100
FB
f
SEL
15k
75
V ADJUST CTRL
OUT
V = 3.3V
IN
LT3905 MONIN
V
IN
220nF
GND
50
100k 100k
V = 5V
LOS IN
APD
ILIM 25
APD
1:10 1:20 1:5
LOS_MON ILIM_MON MON
0
RX POWER
1M
9.09k
0 0.625 1.25 1.875 2.5
4.99k
12.5A LOS
2.75mA
I (mA)
1mV/A APD
LIMIT
3905 TA01b
3905 TA01a
3905fa
1
For more information www.linear.com/LT3905
INPUT CURRENT (mA)
ion pplica
ions pplica
ion uresLT3905
a Te Maxi Mu M r a T p c F T
(Note 1)
TOP VIEW
V , FB, EN/UVLO, CTRL, f ,
IN SEL
LOS_ADJ, LOS, ILIM .................................................12V
V , SW, MONIN, APD ............................................65V
OUT
16 15 14 13
MON, LOS_MON, ILIM_MON ..................................2.5V
ILIM 1 12 CTRL
Operating Ambient Temperature Range
LOS_MON 2 11 EN/UVLO
17
GND
(Note 2) ...................................................... 40 to 125C ILIM_MON V
3 10
IN
MON 4 9 GND
Operating Junction Temperature Range
5 6 7 8
(Note 2) ...................................................... 40 to 125C
Storage Temperature Range ...................... 65 to 125C
UD PACKAGE
16-LEAD (3mm 3mm) PLASTIC QFN
= 68C/W, = 7.5C/W
JA JC
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
o r D i n F Ma T
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3905EUD#PBF LT3905EUD#TRPBF LGGP 16-Lead (3mm 3mm) Plastic QFN 40C to 125C
LT3905IUD#PBF LT3905IUD#TRPBF LGGP 16-Lead (3mm 3mm) Plastic QFN 40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to: