LT3905_15 Datasheet, PDF (1/18 Pages) Linear Technology – Boost DC/DC Converter with APD Current Monitor

LT3905
Boost DC/DC Converter
with APD Current Monitor
Features
n _{65V, 350mA Internal DMOS Switch}
n _{Integrated Schottky Diode}
n _{2% Accurate APD Current Monitoring Over the 3µA}
to 3mA Range
n _{Single Resistor Programs Maximum APD Current}
n _{Fast APD Current Limiter with Indicator}
n _{Programmable Loss-of-Signal Indicator}
n _{CTRL Pin Adjusts Output Voltage}
n _{Programmable VIN Undervoltage Lockout}
n _{High Efficiency Step-Up Converter}
n _{Selectable 1MHz/2MHz Switching Frequency}
n _{Internally Compensated}
n _{Internal Soft-Start}
n _{2.7V to 12V VIN Range}
n _{Low Shutdown Current: <1µA}
Applications
n _{APD Bias}
n _{PIN Diode Bias}
n _{Optical Receivers and Modules}
n _{Fiber Optic Network Equipment}
Description
The LT^®3905 is a fixed frequency current-mode step-up
converter designed to bias avalanche photodiodes (APD)
in optical receivers. The LT3905 features high side APD
current monitoring over four decades of dynamic range
with better than 2% relative accuracy over the 3µA to
3mA range.
The maximum APD current is programmed with a single
resistor, and a fast current limiter with indicator protects
the APD during overload conditions. Adjustable output
voltage provides dynamic bias control, and an adjustable
loss-of-signal indicator flags low APD current.
Coupled with the integrated DMOS power switch and
Schottky rectifier, the LT3905 provides a compact total
solution with few external components and low solution
cost. Constant switching frequency results in predictable
output noise that is easy to filter.
The LT3905 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
V_IN
2.7V to 12V
V_OUT ADJUST
V_IN
100k
Adjustable APD Bias Supply
10µH
1µF
EN/UVLO ^VIN
LOS_ADJ
f_SEL
SW
V_OUT
FB
UP TO 54V
634k
15k
CTRL
100k
LT3905
MONIN
GND
220nF
LOS
APD
ILIM
APD
1:10
1:20
1:5
LOS_MON
ILIM_MON
MON
1M
12.5µA LOS
9.09k
2.75mA
LIMIT
RX POWER
4.99k
1mV/µA
3905 TA01a
Input Current vs APD Current
125
V_APD = 45V
100
75
V_IN = 3.3V
50
V_IN = 5V
25
0
0 0.625 1.25 1.875 2.5
I_APD (mA)
3905 TA01b
For more information www.linear.com/LT3905
3905fa
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