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LT3905EUD#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18
LT3905
1
3905fa
For more information www.linear.com/LT3905
Typical applicaTion
FeaTures DescripTion
Boost DC/DC Converter
with APD Current Monitor
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.
Adjustable APD Bias Supply
Input Current vs APD Current
applicaTions
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 V
IN
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 V
IN
Range
n
Low Shutdown Current: <1µA
n
APD Bias
n
PIN Diode Bias
n
Optical Receivers and Modules
n
Fiber Optic Network Equipment
L, LT , LT C , LT M , Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
LT3905
RX POWER
3905 TA01a
1:5
MON
V
IN
SW
f
SEL
EN/UVLO
CTRL
V
OUT
ADJUST
10µH
1µF
LOS_ADJ
LOS
ILIM
100k100k
V
IN
2.7V to 12V
V
IN
4.99k
1mV/µA
1:20
ILIM_MON
9.09k
2.75mA
LIMIT
1:10
LOS_MON
1M
12.5µA LOS
V
OUT
FB
MONIN
APD
APD
GND
220nF
634k
UP TO 54V
15k
I
APD
(mA)
0
INPUT CURRENT (mA)
75
100
125
2.5
3905 TA01b
50
25
0
0.625
1.25
1.875
V
IN
= 3.3V
V
APD
= 45V
V
IN
= 5V
LT3905
2
3905fa
For more information www.linear.com/LT3905
pin conFiguraTionabsoluTe MaxiMuM raTings
V
IN
, FB, EN/UVLO, CTRL, f
SEL
,
LOS_ADJ, LOS, ILIM .................................................12V
V
OUT
, SW, MONIN, APD ............................................65V
MON, LOS_MON, ILIM_MON ..................................2.5V
Operating Ambient Temperature Range
(Note 2) ...................................................... –40 to 125°C
Operating Junction Temperature Range
(Note 2) ...................................................... –40 to 125°C
Storage Temperature Range ...................... –65 to 125°C
(Note 1)
16 15 14 13
5 6 7 8
TOP VIEW
17
GND
UD PACKAGE
16-LEAD (3mm
×
3mm) PLASTIC QFN
9
10
11
12
4
3
2
1ILIM
LOS_MON
ILIM_MON
MON
CTRL
EN/UVLO
V
IN
GND
f
SEL
FB
LOS_ADJ
LOS
APD
MONIN
SW
V
OUT
θ
JA
= 68°C/W, θ
JC
= 7.5°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3905EUD#PBF LT3905EUD#TRPBF LGGP
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
LT3905IUD#PBF LT3905IUD#TRPBF LGGP
16-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LT C Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
LT3905
3
3905fa
For more information www.linear.com/LT3905
elecTrical characTerisTics
PARAMETER CONDITIONS MIN TYP MAX UNITS
Operating Voltage Range 2.7 12 V
Supply Current V
ENUVLO
= 0V, Device in Shutdown
V
ENUVLO
= 1.1V, Before Trip Point
V
ENUVLO
= 1.3V, V
FB
= 2V, Switcher Standby
V
ENUVLO
= 1.3V, V
FB
= 1.5V, Not Switching
0.1
6
250
650
1
10
350
750
µA
µA
µA
µA
Feedback Voltage (V
FB
) V
CTRL
= 1.5V
l
1.238
1.223
1.248 1.258
1.273
V
V
Feedback Line Regulation 2.7V ≤ V
IN
≤ 12V 0.005 0.025 %/V
FB Pin Bias Current
l
15 75 nA
FB Standby Threshold V
FB
Rising 1.65 1.80 1.95 V
FB Standby Threshold Hysteresis 50 mV
CTRL to FB Offset V
CTRL
= 0.5V
l
–13 0 13 mV
CTRL Input Bias Current Current Out of Pin, V
CTRL
= 0.5V
l
15 75 nA
MON Pin Voltage Clamp I
APD
= 300µA, R
MON
= Open
l
2.35 2.5 V
LOS_MON Pin Voltage Clamp I
APD
= 300µA, R
LOS_MON
= Open
l
2.35 2.5 V
MON Pin Bias Current Current Out of Pin, I
APD
= 0A, V
MON
= 1V 0 nA
LOS_MON Pin Bias Current Current Out of Pin, I
APD
= 0A, V
LOS_MON
= 1V 10 50 nA
ILIM_MON Pin Bias Current Current Out of Pin, I
APD
= 0A, V
ILIM_MON
= 1V 35 175 nA
APD Monitor (MON) Current Gain 300nA ≤ I
APD
≤ 3µA, 12V ≤ MONIN ≤ 65V
3µA ≤ I
APD
≤ 3mA, 12V ≤ MONIN ≤ 65V
l
l
0.185
0.196
0.20
0.20
0.215
0.204
APD Loss of Signal Monitor (LOS_MON)
Current Gain
3µA ≤ I
APD
≤ 30µA, 12V ≤ MONIN ≤ 65V
30µA ≤ I
APD
≤ 3mA, 12V ≤ MONIN ≤ 65V
l
l
0.092
0.096
0.10
0.10
0.108
0.104
APD Current Limit Monitor (ILIM_MON) Current
Gain
30µA ≤ I
APD
≤ 300µA, 12V ≤ MONIN ≤ 65V
300µA ≤ I
APD
≤ 3mA, 12V ≤ MONIN ≤ 65V
l
l
0.045
0.048
0.05
0.05
0.055
0.052
APD Monitor V
oltage Drop MONIN – APD at I
APD
= 3mA, MONIN = 65V 3.7 3.95 4.2 V
Boost Converter
Switching Frequency f
SEL
= 0V
f
SEL
= 2V
l
l
0.9
1.8
1
2
1.1
2.2
MHz
MHz
Maximum Duty Cycle f
SEL
= 0V
f
SEL
= 2V
90
80
95
90
%
%
Switch Current Limit 350 400 450 mA
Switch On-Resistance I
SW
= 150mA 0.75 Ω
Switch Leakage Current SW = 65V 0.1 3 µA
Schottky Forward Voltage I
SCHOTTKY
= 150mA 780 mV
Schottky Reverse Leakage V
OUT
– SW = 65V 3 µA
Loss Of Signal Comparator
Loss of Signal Comparator Internal Threshold LOS_ADJ = 1.5V, LOS_MON Falling 1.185 1.248 1.310 V
Loss of Signal Comparator External Threshold LOS_ADJ = 1.0V, LOS_MON Falling
l
0.950 1.050 V
Loss of Signal Comparator Hysteresis LOS_MON Rising 20 mV
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
ENUVLO
= V
CTRL
= 3.3V unless otherwise noted.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18

LT3905EUD#TRPBF

Mfr. #:
Buy LT3905EUD#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 60V Boost DC-DC Converter with APD Current Monitor
Lifecycle:
New from this manufacturer.
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