LT3905 Datasheet PDF - Linear Technology

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LT3905
Linear Technology

Part Number LT3905
Description Boost DC/DC Converter
Page 16 Pages


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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 five 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
VIN
2.7V to 12V
VOUT ADJUST
VIN
100k
Adjustable APD Bias Supply
10µH
1µF EN/UVLO VIN
LOS_ADJ
fSEL
SW VOUT
FB
UP TO 54V
634k
15k
CTRL
100k
LT3905
MONIN
GND
220nF
LOS
ILIM
1:10
LOS_MON
1:20
ILIM_MON
APD
1:5
MON
APD
1M
12.5µA LOS
9.09k
2.75mA
LIMIT
RX POWER
4.99k
1mV/µA
3905 TA01a
Input Current vs APD Current
125
VAPD = 45V
100
75
VIN = 3.3V
50
VIN = 5V
25
0
0 0.625 1.25 1.875 2.5
IAPD (mA)
3905 TA01b
For more information www.linear.com/LT3905
3905f
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LT3905
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, FB, EN/UVLO, CTRL, fSEL,
LOS_ADJ, LOS, ILIM..................................................12V
VOUT, 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
PIN CONFIGURATION
TOP VIEW
16 15 14 13
ILIM 1
12 CTRL
LOS_MON 2
17 11 EN/UVLO
ILIM_MON 3 GND 10 VIN
MON 4
9 GND
5678
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
θJA = 68°C/W, θJC = 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 LTC 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/
3905f
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LT3905
E LECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VENUVLO = VCTRL = 3.3V unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX
Operating Voltage Range
2.7 12
Supply Current
Feedback Voltage (VFB)
VENUVLO = 0V, Device in Shutdown
VVEENNUUVVLLOO
=
=
1.1V,
1.3V,
Before Trip Point
VFB = 2V, Switcher
Standby
VENUVLO = 1.3V, VFB = 1.5V, Not Switching
VCTRL = 1.5V
1.238
l 1.223
0.1
6
250
650
1.248
1
10
350
750
1.258
1.273
Feedback Line Regulation
FB Pin Bias Current
2.7V ≤ VIN ≤ 12V
0.005
0.025
l 15 75
FB Standby Threshold
FB Standby Threshold Hysteresis
VFB Rising
1.65 1.80 1.95
50
CTRL to FB Offset
CTRL Input Bias Current
MON Pin Voltage Clamp
LOS_MON Pin Voltage Clamp
MON Pin Bias Current
LOS_MON Pin Bias Current
ILIM_MON Pin Bias Current
APD Monitor (MON) Current Gain
APD Loss of Signal Monitor (LOS_MON)
Current Gain
APD Current Limit Monitor (ILIM_MON) Current
Gain
APD Monitor Voltage Drop
Boost Converter
VCTRL = 0.5V
Current Out of Pin, VCTRL = 0.5V
IAPD = 300µA, RMON = Open
IAPD = 300µA, RLOS_MON = Open
Current Out of Pin, IAPD = 0A, VMON = 1V
Current Out of Pin, IAPD = 0A, VLOS_MON = 1V
Current Out of Pin, IAPD = 0A, VILIM_MON = 1V
300nA ≤ IAPD ≤ 3µA, 12V ≤ MONIN ≤ 65V
3µA ≤ IAPD ≤ 3mA, 12V ≤ MONIN ≤ 65V
3µA ≤ IAPD ≤ 30µA, 12V ≤ MONIN ≤ 65V
30µA ≤ IAPD ≤ 3mA, 12V ≤ MONIN ≤ 65V
30µA ≤ IAPD ≤ 300µA, 12V ≤ MONIN ≤ 65V
300µA ≤ IAPD ≤ 3mA, 12V ≤ MONIN ≤ 65V
MONIN – APD at IAPD = 3mA, MONIN = 65V
l –13
0
13
l 15 75
l 2.35 2.5
l 2.35 2.5
0
10 50
35 175
l 0.185 0.20 0.215
l 0.196 0.20 0.204
l 0.092 0.10 0.108
l 0.096 0.10 0.104
l 0.045 0.05 0.055
l 0.048 0.05 0.052
3.7 3.95 4.2
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
fSEL = 0V
fSEL = 2V
fSEL = 0V
fSEL = 2V
l 0.9 1 1.1
l 1.8 2 2.2
90 95
80 90
350 400 450
Switch On-Resistance
Switch Leakage Current
ISW = 150mA
SW = 65V
0.75
0.1 3
Schottky Forward Voltage
Schottky Reverse Leakage
Loss Of Signal Comparator
ISCHOTTKY = 150mA
VOUT – SW = 65V
780
3
Loss of Signal Comparator Internal Threshold LOS_ADJ = 1.5V, LOS_MON Falling
1.185
1.248
1.310
Loss of Signal Comparator External Threshold LOS_ADJ = 1.0V, LOS_MON Falling
l 0.950
1.050
Loss of Signal Comparator Hysteresis
LOS_MON Rising
20
UNITS
V
µA
µA
µA
µA
V
V
%/V
nA
V
mV
mV
nA
V
V
nA
nA
nA
V
MHz
MHz
%
%
mA
Ω
µA
mV
µA
V
V
mV
For more information www.linear.com/LT3905
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LT3905
E LECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VENUVLO = VCTRL = 3.3V unless otherwise noted.
PARAMETER
Current Regulation Buffer Amplifier
ILIM_MON Voltage Regulation Threshold (VIFB)
CONDITIONS
VFB = 0.5V
ILIM_MON APD Current Limit Threshold (VILIM)
ILIM_MON APD Current Limit Line Regulation
ILIM_MON Indicator Threshold
ILIM_MON Indicator Hysteresis
Inputs/Outputs
EN/UVLO Threshold
VAPD = 0V, ∆IAPD/∆VMONIN, 5V < VMONIN < 65V
VILIM_MON Rising
VENUVLO Falling
EN/UVLO Internal Hysteresis
EN/UVLO Hysteresis Current
fSEL Voltage Threshold
fSEL Threshold Hysteresis
fSEL Input Bias Current
LOS Open Drain ON Resistance
LOS Output Low Voltage
LOS Off-State Leakage
ILIM Open Drain ON Resistance
ILIM Output Low Voltage
ILIM Off-State Leakage
VENUVLO Rising
VVEENNUUVVLLOO
=
=
1.1V,
1.3V,
Device
Device
in
in
Shutdown
Operation
fSEL Rising
ILOS = 1mA
ILOS = 2mA
VIN = VLOS = 12V
IILIM = 1mA
IILIM = 2mA
VILIM = 12V
MIN TYP MAX UNITS
1.223
l 1.211
1.248
1.323
l 1.311
1.348
10
l VILIM – 30 VILIM – 10
30
1.273
1.285
1.373
1.385
VILIM – 2
V
V
V
V
μA/V
mV
mV
1.128
l 1.104
0.700
1.200
1.200
25
3
0
0.900
50
0
100
100
1.272
1.296
1.100
0.3
1
0.3
1
V
V
mV
µA
µA
V
mV
µA
Ω
V
µA
Ω
V
µA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT3905E is guaranteed to meet specified performance
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization, and correlation with statistical process controls. The
LT3905I is guaranteed to meet performance specifications over the –40°C
to 125°C operating junction temperature range.
3905f
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