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LTC3426 1.2MHz Step-Up DC/DC Converter in SOT-23
FEATURES

DESCRIPTIO
Internal 2A MOSFET Switch 1.2MHz Switching Frequency Integrated Soft-Start Low 1.6V VIN Operation Low RDS(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 (ThinSOTTM) Package
The LTC(R)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 output 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.
, LT, LTC and LTM 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
APPLICATIO S

White LED Driver Supply Local 3.3V or 5V Supply Battery Back-Up
TYPICAL APPLICATIO
VIN 3.3V 2.2H
3.3V to 5V Boost Converter
100 95 90
SW VIN 10F OFF ON VOUT VOUT 5V 800mA 22F
VIN = 3.3V VOUT = 5V
EFFICIENCY (%)
85 80 75 70 65 60
LTC3426 SHDN GND FB
3426 TA01
55 50 1 10 100 LOAD CURRENT (mA) 1000
3426 TA01b
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Efficiency
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1
LTC3426 ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW SW 1 GND 2 FB 3 6 VIN 5 VOUT 4 SHDN
VIN Voltage ................................................. -0.3V to 6V SW Voltage .................................................. -0.3V to 6V SHDN, FB Voltage ....................................... -0.3V to 6V VOUT ........................................................... -0.3V to 6V Operating Temperature Range (Note 2) .. - 40C to 85C Storage Temperature Range ................. - 65C to 125C Lead Temperature (Soldering, 10 sec)................ 300C
S6 PACKAGE 6-LEAD PLASTIC TSOT-23
TJMAX = 125C, JA = 165C/W, JC = 102C/W
ORDER PART NUMBER LTC3426ES6
S6 PART NUMBER LTAJT
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges.
CO VERTER CHARACTERISTICS
PARAMETER Input Voltage Range Output Voltage Adjust Range Feedback Voltage Feedback Input Current Quiescent Current (Shutdown) Quiescent Current Switch Leakage Switch On Resistance Current Limit Maximum Duty Cycle Switching Frequency SHDN Input High SHDN Input Low SHDN Input Current SHDN = 5.5V VFB = 1.15V VFB = 1.23V CONDITIONS SHDN = VIN
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 1.8V, VOUT = 3.3V, unless otherwise specified.
MIN 1.6 2.25
TYP
MAX 5
UNITS V V V A A A A A %
1.173
1.22
1.247 0.1 1
VSHDN = 0V, Not Including Switch Leakage SHDN = VIN, Not Switching VSW = 5V VOUT = 3.3V VOUT = 5V

600 0.2 0.11 0.10 2 80 0.85 1 2.3 85 1.2
1000 10
1.5 0.4 1
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 LTC3426 is guaranteed to meet performance specifications from 0C to 85C. 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.
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MHz V V A
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LTC3426 TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency vs Temperature
1.40
100
1.3
FREQUENCY (MHz)
EFFICIENCY (%)
IOUT(MAX) (A) 3 VIN (V) 3.4 3.8
1.2
1.1
1.0 -50
-30
-10 10 30 50 TEMPERATURE (C)
RDS(ON) vs Temperature
0.15 0.14 0.13 VOUT = 2.5V
FB VOLTAGE (V)
0.12
RDS(ON) ()
0.11 0.10 0.09 0.08 0.07 0.06 0.05 -50 -25
VOUT = 5V VOUT = 3.3V
25 50 0 TEMPERATURE (C)
SW Pin Antiringing Operation
VOUT 500mV/DIV IOUT 200mA/DIV
SW 1V/DIV
IL 50mA/DIV
VIN = 1.8V VOUT = 3.3V
UW
70 90
3426 G01
Efficiency vs VIN
FIGURE 1 CIRCUIT 98 TA = 25C ILOAD = 150mA 96 V OUT = 5V 94 COUT = 22F L = 2.2H 92 90 88 86 84 82 80 1.8 2.2 2.6 4.2 0.3 0.5 1.3
IOUT(MAX) vs VIN
FIGURE 1 CIRCUIT TA = 25C VOUT = 5V 1.1 C OUT = 22F L = 2.2H 0.9
0.7
1.8
2.2
2.6
3 VIN (V)
3.4
3.8
4.2
3426 G03
LT1108 * TPC12
FB Pin Voltage
1.25 1.24 1.23 1.22 1.21 1.20 1.19 -50
IL 200mA/DIV VOUT 500mV/DIV
Switching Waveforms
SW 2V/DIV
75
100
3426 G04
-25
0 25 50 TEMPERATURE (C)
75
100
3426 G05
VIN = 1.8V VOUT = 3.3V COUT = 22F L = 2.5H
100ns/DIV
3426 G06
VOUT Transient Response
500mA 250mA
IL 500mA/DIV
100ns/DIV
3426 G07
VIN = 1.8V VOUT = 3.3V COUT = 22F L = 2.5H
40s/DIV
3426 G08
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LTC3426
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor between SW and VIN. A Schottky diode is connected between SW and VOUT. 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 VIN 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 gm Error Amplifier. Connect resistor divider tap to this pin. The output voltage can be adjusted from 2.5V to 5V by: R1 VOUT = 1.22 * 1 + R2 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 VIN through a 1M pull-up resistor. VOUT (Pin 5): Output Voltage Sense Input. The NMOS switch gate drive is derived from the greater of VOUT and VIN. VIN (Pin 6): Input Supply. Must be locally bypassed.
BLOCK DIAGRA
1.22V REFERENCE
VOUT R1 (EXTERNAL) FB R2 (EXTERNAL)
-
RAMP GENERATOR
SHDN 4 SHUTDOWN AND SOFT-START 1.2MHz OSCILLATOR 2 GND
3426 F01
Figure 1
4
+
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VOUT
VIN 6
SW 1
+
A1
COMPARATOR
5
-
RC CC A2 PWM LOGIC AND DRIVER
-
3 FB
+
0.02
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LTC3426
OPERATIO
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 RDS(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
APPLICATIO S I FOR ATIO
Setting the Output Voltage
The output voltage, VOUT, is set by a resistive divider from VOUT to ground. The divider tap is tied to the FB pin. VOUT is set by the formula: R1 VOUT = 1.22 * 1 + R2 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 applications. Larger values of inductance will allow greater output current capability by reducing the inductor ripple current. Increasing the inductance above 3.3H will increase component size while providing little improvement in output current capability. The inductor current ripple is typically set for 20% to 40% of the maximum inductor current (IP). High frequency ferrite core inductor materials reduce frequency dependent power losses compared to cheaper powdered iron types, improving efficiency. The inductor should have low DCR (DC resistance)
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control voltage at the output of the error amplifier is the amplified and compensated difference between the feedback 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 ILIMIT 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. to reduce the I2R 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 Sumida Murata www.tdk.com www.sumida.com 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 preferred 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
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LTC3426
APPLICATIO S I FOR ATIO
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 manufacturers for detailed information in their entire selection of ceramic parts.
Table 2. Ceramic Capacitor Manufacturers
Taiyo Yuden Murata TDK www.t-yuden.com www.murata.com 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 Schottky diode rated at 2A is recommended for use with the LTC3426.
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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.
VIN 1 2 3 SW VIN 6 5 4 GND VOUT FB SHDN VOUT
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Figure 2. Recommended Component Placement for Single Layer Board
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LTC3426
TYPICAL APPLICATIO S
Efficiency
L1 2.2H VIN 3.3V SW VIN C1 10F OFF ON VOUT R1 95.3k 1% R2 30.9k 1%
3426 TA02a
EFFICIENCY (%)
LTC3426 SHDN GND FB
C1: TAIYO YUDEN X5R JMK212BJ475ML C2: TAIYO YUDEN X5R JMK316BJ226ML D1: ON SEMICONDUCTOR MBRA210LT3 L1: COILCRAFT D03316P-222
L1 1.5H VIN 1.8V SW VIN C1 10F OFF ON VOUT
D1
EFFICIENCY (%)
LTC3426 SHDN GND FB
C1: TDK C1608X5R0J106M C2: TAIYO YUDEN JMK316BJ226ML D1: ON SEMICONDUCTOR MBRM120LT3 L1: TDK RLF7030T-1R5N6R1
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D1
100 95 90
VOUT 5V 800mA
85 80 75 70 65 60 55 50 1 10 100 LOAD CURRENT (mA) 1000
3426 TA02b
C2 22F
Efficiency
100
90
VOUT 2.5V 800mA C2 22F
R1 64.9k 1% R2 61.9k 1%
80
70
60
3426 TA03a
50 1 10 100 LOAD CURRENT (mA) 1000
3426 TA03b
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LTC3426
TYPICAL APPLICATIO S
Efficiency
VIN 3V TO 4.2V L1 2.2H
100
D1
SW VIN C1 10F OFF ON VOUT R1 95.3k 1% R2 30.9k 1%
EFFICIENCY (%)
LTC3426 SHDN GND FB
C1: TDK C1608X5R0J475M C2: TAIYO YUDEN JMK316BJ226ML D1: ON SEMICONDUCTOR MBR120VLSFT1 L1: SUMIDA CDRH4D28-2R2 2
VIN 2.5V
L1 2.5H
D1
VIN C1 10F OFF ON
VOUT
EFFICIENCY (%)
SW R1 75k 1% R2 44.2k 1%
LTC3426 SHDN GND FB
C1: TDK C1608X5R0J106 C2: TAIYO YUDEN JMK316BJ266 D1: ON SEMICONDUCTOR MBRM120LT3 L1: SUMIDA CDRH5D28-2R5 2
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VOUT 5V 750mA AT 3V C2 22F
85 80 75 70 65 60 VIN = 3V
3426 TA04a
55 50 1 10 100 LOAD CURRENT (mA) 1000
3426 TA04b
Efficiency
100
90
VOUT 3.3V 800mA C2 22F
80
70
60
3426 TA05a
50 1 10 100 LOAD CURRENT (mA) 1000
3426 TA05b
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LTC3426
TYPICAL APPLICATIO S
Efficiency
L1 1.5H VIN 1.8V
EFFICIENCY (%) 100
D1
90
SW VIN C1 10F OFF ON VOUT R1 75k 1% R2 44.2k 1%
LTC3426 SHDN GND FB
C1: TDK C1608X5R0J106M C2: TAIYO YUDEN JMK316BJ226ML D1: ON SEMICONDUCTOR MBRM120LT3 L1: TDK RLF7030T-1R5N6R1
VIN 1.8V
L1 2.2H
D1
80
SW VIN C1 10F OFF ON VOUT R1 95.3k 1% R2 30.9k 1%
EFFICIENCY (%)
LTC3426 SHDN GND FB
C1: TDK C1608X5R0J475M C2: TAIYO YUDEN JMK316BJ226ML D1: ON SEMICONDUCTOR MBR120VLSFT1 L1: SUMIDA CDRH4D28-2R2 2
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VOUT 3.3V 540mA C2 22F
80
70
60
3426 TA06a
50 1 10 100 LOAD CURRENT (mA) 1000
3426 TA06b
Efficiency
90
VOUT 5V 400mA C2 22F
70
60
50
3426 TA07a
40 1 10 100 LOAD CURRENT (mA) 1000
3426 TA07b
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LTC3426
TYPICAL APPLICATIO S
Efficiency
VIN 2.5V L1 2.5H D1
SW VIN C1 10F OFF ON VOUT R1 95.3k 1% R2 30.9k 1%
EFFICIENCY (%)
LTC3426 SHDN GND FB
C1: TDK C1608X5R0J106 C2: TAIYO YUDEN JMK316BJ266 D1: ON SEMICONDUCTOR MBRM120LT3 L1: SUMIDA CDRH5D28-2R5
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100
90
VOUT 5V 550mA C2 22F
80
70
60
3426 TA08a
50 1 10 100 LOAD CURRENT (mA) 1000
3426 TA08b
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LTC3426
PACKAGE DESCRIPTIO U
S6 Package 6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636 Rev B)
0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE ID 0.95 BSC 0.30 - 0.45 6 PLCS (NOTE 3) 0.80 - 0.90 0.20 BSC 1.00 MAX DATUM `A' 0.01 - 0.10 0.09 - 0.20 (NOTE 3) 1.90 BSC
S6 TSOT-23 0302 REV B
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.30 - 0.50 REF
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 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
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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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LTC3426 RELATED PARTS
PART NUMBER LT1613 LT1946/LT1946A LTC3400/LTC3400B LTC3401/LTC3402 LTC3421 LTC3425 LTC3429 LTC3436 LTC3459 LTC3464 DESCRIPTION 550mA (ISW), 1.4MHz, High Efficiency Step-Up DC/DC Converter 1.5A (ISW), 1.2MHz/2.7MHz, High Efficiency Step-Up DC/DC Converter 600mA (ISW), 1.2MHz, Synchronous Step-Up DC/DC Converter 1A/2A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter 3A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 5A (ISW), 8MHz, 4-Phase Synchronous Step-Up DC/DC Converter with Output Disconnect 600mA (ISW), 550kHz, Synchronous Step-Up DC/DC Converter with Soft-Start/Output Disconnect 3A (ISW), 1MHz, High Efficiency Step-Up DC/DC Converter 75mA (ISW), 10V Micropower Synchronous Boost Converter in ThinSOT 85mA (ISW), High Efficiency Step-Up DC/DC Converter with Schottky and PNP Disconnect COMMENTS 90% Efficiency, VIN: 0.9V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD < 1A, ThinSOT High Efficiency, VIN: 2.45V to 16V, VOUT(MAX) = 34V, IQ = 3.2mA, ISD < 1A, MS8 92% Efficiency, VIN: 0.5V to 5V, VOUT(MAX) = 5V, IQ = 19A/300A, ISD < 1A, ThinSOT 97% Efficiency, VIN: 0.5V to 5V, VOUT(MAX) = 5.5V, IQ = 38A, ISD < 1A, MS10 95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12A, ISD < 1A, QFN24 95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12A, ISD < 1A, QFN32 90% Efficiency, VIN: 0.5V to 4.3V, VOUT(MAX) = 5V, IQ = 20A, ISD < 1A, ThinSOT VIN: 3V to 25V, VOUT(MAX) = 34V, IQ = 0.9mA, ISD < 6A, TSSOP16E VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10A, ISD < 1A, ThinSOT VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25A, ISD < 1A, ThinSOT
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT 0307 REV A * PRINTED IN THE USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2004

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