1
LTC3426
3426f
1.2MHz Step-Up DC/DC
Converter in SOT-23
Internal 2A MOSFET Switch
1.2MHz Switching Frequency
Integrated Soft-Start
V
IN
Range: 1.6V to 4.3V
Low R
DS(ON)
Switch: 100m at 5V Output
Delivers 5V at 800mA from a 3.3V Input
Delivers 3.3V at 800mA from a 2.5V Input
Uses Small, Low Profile External Components
Low Profile (1mm) SOT-23 (ThinSOT
TM
) Package
White LED Driver Supply
Local 3.3V or 5V Supply
Battery Back-Up
The LTC
3426 step-up switching regulator generates an
output voltage of up to 5.5V from an input voltage as low
as 1.6V. Ideal for applications where space is limited, it
switches at 1.2MHz, allowing the use of tiny, low cost and
low profile external components. Its internal 2A, 100m
NMOS switch provides high efficiency even at heavy load,
while the constant frequency, current mode architecture
results in low, predictable output noise that is easy to filter.
Antiringing circuitry reduces EMI concerns by damping
the inductor while in discontinuous mode, and internal
soft-start eases inrush current worries. Internal frequency
compensation is designed to accommodate ceramic out-
put capacitors, further reducing noise. The device features
very low shutdown current of 0.5A.
The LTC3426 is available in the 6-lead SOT-23 package.
3.3V to 5V Boost Converter
Efficiency
SW
2.2H
V
IN
3.3V
V
IN
LTC3426
SHDN
22F
10F
V
OUT
5V
800mA
3426 TA01
V
OUT
FB
OFF ON
GND
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
LOAD CURRENT (mA)
1
70
EFFICIENCY (%)
75
80
85
90
10
100
1000
3426 TA01b
65
60
55
50
95
100
V
IN
= 3.3V
V
OUT
= 5V
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 6498466, 6611131
2
LTC3426
3426f
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
V
IN
Voltage ................................................. 0.3V to 6V
SW Voltage .................................................. 0.3V to 6V
SHDN, FB Voltage ....................................... 0.3V to 6V
V
OUT
........................................................... 0.3V to 6V
Operating Temperature Range (Note 2) .. 40C to 85C
Storage Temperature Range ................. 65C to 125C
Lead Temperature (Soldering, 10 sec)................ 300C
T
JMAX
= 125C,
JA
= 165C/W,
JC
= 102C/W
(Note 1)
ORDER PART
NUMBER
LTC3426ES6
Consult LTC Marketing for parts specified with wider operating temperature ranges.
PACKAGE/ORDER I FOR ATIO
U
U
W
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage Range
SHDN = V
IN
1.6
4.3
V
Output Voltage Adjust Range
2.25
5
V
Feedback Voltage
1.173
1.22
1.247
V
Feedback Input Current
V
FB
= 1.23V
0.1
A
Quiescent Current (Shutdown)
V
SHDN
= 0V, Not Including Switch Leakage
1
A
Quiescent Current
SHDN = V
IN
, Not Switching
600
1000
A
Switch Leakage
V
SW
= 5V
0.2
10
A
Switch On Resistance
V
OUT
= 3.3V
0.11
V
OUT
= 5V
0.10
Current Limit
2
2.3
A
Maximum Duty Cycle
V
FB
= 1.15V
80
85
%
Switching Frequency
0.85
1.2
1.5
MHz
SHDN Input High
1
V
SHDN Input Low
0.4
V
SHDN Input Current
SHDN = 5.5V
1
A
The
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25C. V
IN
= 1.8V, V
OUT
= 3.3V, unless otherwise specified.
CO VERTER CHARACTERISTICS
U
SW 1
GND 2
FB 3
6 V
IN
5 V
OUT
4 SHDN
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
S6 PART
MARKING
LTAJT
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3426 is guaranteed to meet performance specifications
from 0C to 70C. Specifications over the 40C to 85C operating
temperature are assured by design, characterization and correlation with
statistical process controls.
Note 3: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
3
LTC3426
3426f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Oscillator Frequency
vs Temperature
TEMPERATURE (C)
50
1.0
FREQUENCY (MHz)
1.1
1.2
1.3
1.40
30
10
10
30
3426 G01
50
70
90
V
IN
(V)
1.8
80
EFFICIENCY (%)
84
88
92
2.2
2.6
3
3.4
LT1108 TPC12
3.8
96
100
82
86
90
94
98
4.2
FIGURE 1 CIRCUIT
T
A
= 25C
I
LOAD
= 150mA
V
OUT
= 5V
C
OUT
= 22F
L = 2.2H
V
IN
(V)
1.8
0.3
I
OUT(MAX)
(A)
0.5
0.7
0.9
1.1
1.3
2.2
2.6
3
3.4
3426 G03
3.8
4.2
FIGURE 1 CIRCUIT
T
A
= 25C
V
OUT
= 5V
C
OUT
= 22F
L = 2.2H
Efficiency vs V
IN
I
OUT(MAX)
vs V
IN
R
DS(ON)
vs Temperature
TEMPERATURE (C)
50
0.05
R
DS(ON)
(
)
0.07
0.09
0.11
25
0
25
50
3426 G04
75
0.13
0.15
0.06
0.08
0.10
0.12
0.14
100
V
OUT
= 2.5V
V
OUT
= 5V
V
OUT
= 3.3V
TEMPERATURE (C)
50
1.19
FB VOLTAGE (V)
1.20
1.21
1.22
1.23
1.25
25
0
25
50
3426 G05
75
100
1.24
FB Pin Voltage
V
OUT
500mV/DIV
SW
2V/DIV
100ns/DIV
V
IN
= 1.8V
V
OUT
= 3.3V
C
OUT
= 22F
L = 2.5H
3426 G06
I
L
200mA/DIV
Switching Waveforms
SW Pin Antiringing Operation
V
OUT
Transient Response
SW
1V/DIV
100ns/DIV
V
IN
= 1.8V
V
OUT
= 3.3V
3426 G07
I
L
50mA/DIV
40s/DIV
V
IN
= 1.8V
V
OUT
= 3.3V
C
OUT
= 22F
L = 2.5H
3426 G08
I
L
500mA/DIV
I
OUT
200mA/DIV
V
OUT
500mV/DIV
250mA
500mA
4
LTC3426
3426f
U
U
U
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor between SW and
V
IN
. A Schottky diode is connected between SW and V
OUT
.
Keep these PCB trace lengths as short and wide as
possible to reduce EMI and voltage overshoot. If the
inductor current falls to zero, an internal 100 antiringing
switch is connected from SW to V
IN
to minimize EMI.
GND (Pin 2): Signal and Power Ground. Provide a short
direct PCB path between GND and the () side of the output
capacitor(s).
FB (Pin 3): Feedback Input to the g
m
Error Amplifier.
Connect resistor divider tap to this pin. The output voltage
can be adjusted from 2.5V to 5V by:
V
R
R
OUT
=
+
1 22
1
1
2
.
SHDN (Pin 4): Logic Controlled Shutdown Input.
SHDN = High: Normal free running operation
SHDN = Low: Shutdown, quiescent current < 1A
Typically, SHDN should be connected to V
IN
through a 1M
pull-up resistor.
V
OUT
(Pin 5): Output Voltage Sense Input. The NMOS
switch gate drive is derived from the greater of V
OUT
and
V
IN
.
V
IN
(Pin 6): Input Supply. Must be locally bypassed.
BLOCK DIAGRA
W
Figure 1
4
SHUTDOWN AND
SOFT-START
1.22V
REFERENCE
RAMP
GENERATOR
1.2MHz
OSCILLATOR
3426 F01
PWM LOGIC
AND DRIVER
+
3
FB
FB
V
OUT
SHDN
SW
A1
+
+
A2
R
C
R2 (EXTERNAL)
R1 (EXTERNAL)
0.02
C
C
1
GND
2
V
IN
6
V
OUT
COMPARATOR
5
5
LTC3426
3426f
OPERATIO
U
The LTC3426 is a monolithic 1.2MHz boost converter
housed in a 6-lead SOT-23 package. The device features
fixed frequency, current mode PWM control for excellent
line and load regulation. The low R
DS(ON)
NMOS switch
enables the device to maintain high efficiency over a wide
range of load current. Operation of the feedback loop
which sets the peak inductor current to keep the output in
regulation can be best understood by referring to the Block
Diagram in Figure 1. At the start of each clock cycle a latch
in the PWM logic is set and the NMOS switch is turned on.
The sum of a voltage proportional to the switch current
and a slope compensating voltage ramp is fed to the
positive input to the PWM comparator. When this voltage
exceeds either a voltage proportional to the 2A current
limit or the PWM control voltage, the latch in the PWM
logic is reset and NMOS switch is turned off. The PWM
control voltage at the output of the error amplifier is the
amplified and compensated difference between the feed-
back voltage on the FB pin and the internal reference
voltage of 1.22V. If the control voltage increases, more
current is delivered to the output. When the control voltage
exceeds the I
LIMIT
reference voltage, the peak current is
limited to a minimum of 2A. The current limit helps protect
the LTC3426 internal switch and external components
connected to it. If the control voltage decreases, less
current is delivered to the output. During load transients
control voltage may decrease to the point where no
switching occurs until the feedback voltage drops below
the reference. The LTC3426 has an integrated soft-start
feature which slowly ramps up the feedback control node
from 0V. The soft-start is initiated when SHDN is pulled
high.
APPLICATIO S I FOR ATIO
W
U
U
U
Setting the Output Voltage
The output voltage, V
OUT
, is set by a resistive divider from
V
OUT
to ground. The divider tap is tied to the FB pin. V
OUT
is set by the formula:
V
R
R
OUT
=
+
1 22
1
1
2
.
Inductor Selection
The LTC3426 can utilize small surface mount inductors
due to its 1.2MHz switching frequency. A 1.5H or 2.2H
inductor will be the best choice for most LTC3426 appli-
cations. Larger values of inductance will allow greater
output current capability by reducing the inductor ripple
current. Increasing the inductance above 3.3H will in-
crease component size while providing little improve-
ment in output current capability. The inductor current
ripple is typically set for 20% to 40% of the maximum
inductor current (I
P
). High frequency ferrite core inductor
materials reduce frequency dependent power losses com-
pared to cheaper powdered iron types, improving effi-
ciency. The inductor should have low DCR (DC resistance)
to reduce the I
2
R power losses, and must be able to
handle the peak inductor current without saturating.
Several inductor manufacturers are listed in Table 1.
Table 1. Inductor Manufacturers
TDK
www.tdk.com
Sumida
www.sumida.com
Murata
www.murata.com
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used to minimize the output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
extremely low ESR and are available in small footprints. A
15F to 30F output capacitor is sufficient for most
applications. X5R and X7R dielectric materials are pre-
ferred for their ability to maintain capacitance over wide
voltage and temperature ranges.
Low ESR input capacitors reduce input switching noise
and reduce the peak current drawn from the input supply.
It follows that ceramic capacitors are also a good choice
for input decoupling and should be located as close as
6
LTC3426
3426f
possible to the device. A 10F input capacitor is sufficient
for most applications. Table 2 shows a list of several
ceramic capacitor manufacturers. Consult the manufac-
turers for detailed information in their entire selection of
ceramic parts.
Table 2. Ceramic Capacitor Manufacturers
Taiyo Yuden
www.t-yuden.com
Murata
www.murata.com
TDK
www.component.tdk.com
Diode Selection
A Schottky diode is recommended for use with the LTC3426.
Use of a low forward voltage diode such as the ON
Semiconductor MBRA210LT3 is recommended. A Schot-
tky diode rated at 2A is recommended for use with the
LTC3426.
APPLICATIO S I FOR ATIO
W
U
U
U
PCB Layout Guidelines
The high speed operation of the LTC3426 demands careful
attention to board layout. You will not get advertised
performance with careless layout. Figure 2 shows the
recommended component placement. A large ground pin
copper area will help to lower the chip temperature.
Figure 2. Recommended Component Placement
for Single Layer Board
SW
V
IN
V
OUT
3426 F02
GND
FB
V
IN
V
OUT
SHDN
1
2
3
6
5
4
7
LTC3426
3426f
TYPICAL APPLICATIO S
U
Efficiency
SW
V
IN
1.8V
V
IN
LTC3426
SHDN
V
OUT
2.5V
800mA
3426 TA03a
V
OUT
FB
OFF ON
GND
L1
1.5H
D1
C2
22F
C1
10F
R1
64.9k
1%
R2
61.9k
1%
C1: TDK C1608X5R0J106M
C2: TAIYO YUDEN JMK316BJ226ML
D1: ON SEMICONDUCTOR MBRM120LT3
L1: TDK RLF7030T-1R5N6R1
Efficiency
SW
L1
2.2H
D1
V
IN
3.3V
V
IN
LTC3426
SHDN
C2
22F
C1
10F
V
OUT
5V
800mA
R1
95.3k
1%
R2
30.9k
1%
C1: TAIYO YUDEN X5R JMK212BJ475ML
C2: TAIYO YUDEN X5R JMK316BJ226ML
D1: ON SEMICONDUCTOR MBRA210LT3
L1: COILCRAFT D03316P-222
3426 TA02a
V
OUT
FB
OFF ON
GND
LOAD CURRENT (mA)
1
70
EFFICIENCY (%)
75
80
85
90
10
100
1000
3426 TA02b
65
60
55
50
95
100
LOAD CURRENT (mA)
1
50
EFFICIENCY (%)
80
90
100
10
100
1000
3426 TA03b
70
60
8
LTC3426
3426f
TYPICAL APPLICATIO S
U
SW
V
IN
2.5V
V
IN
LTC3426
SHDN
V
OUT
3.3V
800mA
3426 TA05a
V
OUT
FB
OFF ON
GND
L1
2.5H
D1
C2
22F
C1
10F
R1
75k
1%
R2
44.2k
1%
C1: TDK C1608X5R0J106
C2: TAIYO YUDEN JMK316BJ266
D1: ON SEMICONDUCTOR MBRM120LT3
L1: SUMIDA CDRH5D28-2R5 2
Efficiency
SW
V
IN
3V TO 4.2V
V
IN
LTC3426
SHDN
V
OUT
5V
750mA AT 3V
3426 TA04a
V
OUT
FB
OFF ON
GND
L1
2.2H
D1
C2
22F
C1
10F
R1
95.3k
1%
R2
30.9k
1%
C1: TDK C1608X5R0J475M
C2: TAIYO YUDEN JMK316BJ226ML
D1: ON SEMICONDUCTOR MBR120VLSFT1
L1: SUMIDA CDRH4D28-2R2 2
Efficiency
LOAD CURRENT (mA)
1
70
EFFICIENCY (%)
75
80
85
90
10
100
1000
3426 TA04b
65
60
55
50
95
100
V
IN
= 4.2V
V
IN
= 3V
LOAD CURRENT (mA)
1
50
EFFICIENCY (%)
80
90
100
10
100
1000
3426 TA05b
70
60
9
LTC3426
3426f
TYPICAL APPLICATIO S
U
Efficiency
Efficiency
SW
V
IN
1.8V
V
IN
LTC3426
SHDN
V
OUT
3.3V
540mA
3426 TA06a
V
OUT
FB
OFF ON
GND
L1
1.5H
D1
C2
22F
C1
10F
R1
75k
1%
R2
44.2k
1%
C1: TDK C1608X5R0J106M
C2: TAIYO YUDEN JMK316BJ226ML
D1: ON SEMICONDUCTOR MBRM120LT3
L1: TDK RLF7030T-1R5N6R1
SW
V
IN
1.8V
V
IN
LTC3426
SHDN
V
OUT
5V
400mA
3426 TA07a
V
OUT
FB
OFF ON
GND
L1
2.2H
D1
C2
22F
C1
10F
R1
95.3k
1%
R2
30.9k
1%
C1: TDK C1608X5R0J475M
C2: TAIYO YUDEN JMK316BJ226ML
D1: ON SEMICONDUCTOR MBR120VLSFT1
L1: SUMIDA CDRH4D28-2R2 2
LOAD CURRENT (mA)
1
50
EFFICIENCY (%)
80
90
100
10
100
1000
3426 TA06b
70
60
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
70
80
90
10
100
1000
3426 TA07b
60
50
10
LTC3426
3426f
TYPICAL APPLICATIO S
U
Efficiency
SW
V
IN
2.5V
V
IN
LTC3426
SHDN
V
OUT
5V
550mA
3426 TA08a
V
OUT
FB
OFF ON
GND
L1
2.5H
D1
C2
22F
C1
10F
R1
95.3k
1%
R2
30.9k
1%
C1: TDK C1608X5R0J106
C2: TAIYO YUDEN JMK316BJ266
D1: ON SEMICONDUCTOR MBRM120LT3
L1: SUMIDA CDRH5D28-2R5
LOAD CURRENT (mA)
1
50
EFFICIENCY (%)
80
90
100
10
100
1000
3426 TA08b
70
60
11
LTC3426
3426f
U
PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
1.50 1.75
(NOTE 4)
2.80 BSC
0.30 0.45
6 PLCS (NOTE 3)
DATUM `A'
0.09 0.20
(NOTE 3)
S6 TSOT-23 0302
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 0.90
1.00 MAX
0.01 0.10
0.20 BSC
0.30 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
3.85 MAX
0.62
MAX
0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
12
LTC3426
3426f
LINEAR TECHNOLOGY CORPORATION 2004
LT/TP 1104 1K PRINTED IN THE USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
FAX: (408) 434-0507
www.linear.com
PART NUMBER
DESCRIPTION
COMMENTS
LT1613
550mA (I
SW
), 1.4MHz, High Efficiency Step-Up
90% Efficiency, V
IN
: 0.9V to 10V, V
OUT(MAX)
= 34V, I
Q
= 3mA,
DC/DC Converter
I
SD
< 1A, ThinSOT
LT1946/LT1946A
1.5A (I
SW
), 1.2MHz/2.7MHz, High Efficiency Step-Up
High Efficiency, V
IN
: 2.45V to 16V, V
OUT(MAX)
= 34V, I
Q
= 3.2mA,
DC/DC Converter
I
SD
< 1A, MS8
LTC3400/LTC3400B
600mA (I
SW
), 1.2MHz, Synchronous Step-Up
92% Efficiency, V
IN
: 0.5V to 5V, V
OUT(MAX)
= 5V, I
Q
= 19A/300A,
DC/DC Converter
I
SD
< 1A, ThinSOT
LTC3401/LTC3402
1A/2A (I
SW
), 3MHz, Synchronous Step-Up DC/DC
97% Efficiency, V
IN
: 0.5V to 5V, V
OUT(MAX)
= 5.5V, I
Q
= 38A,
Converter
I
SD
< 1A, MS10
LTC3421
3A (I
SW
), 3MHz, Synchronous Step-Up DC/DC Converter
95% Efficiency, V
IN
: 0.5V to 4.5V, V
OUT(MAX)
= 5.25V, I
Q
= 12A,
with Output Disconnect
I
SD
< 1A, QFN24
LTC3425
5A (I
SW
), 8MHz, 4-Phase Synchronous Step-Up DC/DC
95% Efficiency, V
IN
: 0.5V to 4.5V, V
OUT(MAX)
= 5.25V, I
Q
= 12A,
Converter with Output Disconnect
I
SD
< 1A, QFN32
LTC3429
600mA (I
SW
), 550kHz, Synchronous Step-Up
90% Efficiency, V
IN
: 0.5V to 4.3V, V
OUT(MAX)
= 5V, I
Q
= 20A,
DC/DC Converter with Soft-Start/Output Disconnect
I
SD
< 1A, ThinSOT
LTC3436
3A (I
SW
), 1MHz, High Efficiency Step-Up DC/DC Converter V
IN
: 3V to 25V, V
OUT(MAX)
= 34V, I
Q
= 0.9mA, I
SD
< 6A, TSSOP16E
LTC3459
75mA (I
SW
), 10V Micropower Synchronous Boost
V
IN
: 1.5V to 5.5V, V
OUT(MAX)
= 10V, I
Q
= 10A, I
SD
< 1A, ThinSOT
Converter in ThinSOT
LTC3464
85mA (I
SW
), High Efficiency Step-Up DC/DC Converter
V
IN
: 2.3V to 10V, V
OUT(MAX)
= 34V, I
Q
= 25A, I
SD
< 1A, ThinSOT
with Schottky and PNP Disconnect
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