LINEAR TECHNOLOGY LTC3426 Technical data

FEATURES

■

Internal 2A MOSFET Switch

■

1.2MHz Switching Frequency

■

Integrated Soft-Start

■

Low 1.6V VIN Operation

■

Low R

■

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

Switch: 100mΩ at 5V Output

DS(ON)

U

APPLICATIO S

■

White LED Driver Supply

■

Local 3.3V or 5V Supply

■

Battery Back-Up

LTC3426

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

U

DESCRIPTIO

®

The LTC
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, 100mΩ
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 0.5µA.

3426 step-up switching regulator generates an

TYPICAL APPLICATIO

3.3V to 5V Boost Converter Efficiency

V

3.3V

IN

10µF

2.2µH

V

SHDN

SW

IN

LTC3426

GND

V

OUT

FBOFF ON

U

22µF

3426 TA01

V

OUT

5V
800mA

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

100

VIN = 3.3V

95

= 5V

V

OUT

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

1

10 100 1000

LOAD CURRENT (mA)

3426 TA01b

3426fa

1

LTC3426

W

O

A

(Note 1)

LUTEXI TIS

S

VIN Voltage ................................................. –0.3V to 6V

SW Voltage .................................................. – 0.3V to 6V

SHDN, FB Voltage ....................................... – 0.3V to 6V

V

........................................................... – 0.3V to 6V

OUT

Operating Temperature Range (Note 2) .. –40°C to 85°C

Storage Temperature Range ................. –65°C to 125°C

Lead Temperature (Soldering, 10 sec)................ 300°C

A

WUW

U

ARB

G

PACKAGE/ORDER I FOR ATIO

TOP VIEW

SW 1

GND 2

FB 3

S6 PACKAGE

6-LEAD PLASTIC TSOT-23

T

= 125°C, θJA = 165°C/W, θJC = 102°C/W

JMAX

ORDER PART NUMBER

UU

6 V

IN

5 V

OUT

4 SHDN

W

S6 PART NUMBER

LTC3426ES6 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.

U

CO VERTER CHARACTERISTICS

temperature range, otherwise specifications are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Voltage Range SHDN = V

Output Voltage Adjust Range 2.25 5 V

Feedback Voltage

Feedback Input Current VFB = 1.23V 0.1 µA

Quiescent Current (Shutdown) V

Quiescent Current SHDN = VIN, Not Switching 600 1000 µA

Switch Leakage VSW = 5V 0.2 10 µA

Switch On Resistance V

Current Limit

Maximum Duty Cycle VFB = 1.15V 80 85 %

Switching Frequency

SHDN Input High 1V

SHDN Input Low 0.4 V

SHDN Input Current SHDN = 5.5V 1 µA

V

SHDN

OUT
OUT

A

IN

= 0V, Not Including Switch Leakage 1 µA

= 3.3V 0.11 Ω
= 5V 0.10 Ω

The ● denotes the specifications which apply over the full operating

= 25°C. VIN = 1.8V, V

= 3.3V, unless otherwise specified.

OUT

1.6 V

●

1.173 1.22 1.247 V

●

●

2 2.3 A

0.85 1.2 1.5 MHz

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 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature are assured by design, characterization and correlation with
statistical process controls.

2

Note 3: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.

3426fa

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Oscillator Frequency
vs Temperature

1.40

1.3

1.2

FREQUENCY (MHz)

1.1

1.0
–30 –10 10 30

–50

TEMPERATURE (°C)

50 70 90

3426 G01

Efficiency vs V

100

FIGURE 1 CIRCUIT

98

= 25°C

T

A

= 150mA

I

LOAD

96

= 5V

V

OUT

= 22µF

C

OUT

94

L = 2.2µH

92

90

88

EFFICIENCY (%)

86

84

82

80

1.8

2.2

2.6

IN

3 3.4

VIN (V)

3.8

LT1108 • TPC12

4.2

I

OUT(MAX)

1.3
FIGURE 1 CIRCUIT

T
V

1.1
C

L = 2.2µH

0.9

(A)

OUT(MAX)

0.7

I

0.5

0.3

1.8

= 25°C

A
OUT
OUT

vs V

= 5V
= 22µF

2.6 3 3.4

2.2

LTC3426

IN

3.8 4.2

VIN (V)

3426 G03

0.15

0.14

0.13

0.12

0.11

(Ω)

0.10

DS(ON)

0.09

R

0.08

0.07

0.06

0.05

R

–50

vs Temperature

DS(ON)

–25

TEMPERATURE (°C)

1V/DIV

50mA/DIV

V

= 2.5V

OUT

V

= 5V

OUT

V

= 3.3V

OUT

0

25 50

75

100

3426 G04

SW Pin Antiringing Operation

SW

I

L

V

= 1.8V

IN
OUT

= 3.3V

100ns/DIVV

FB Pin Voltage

1.25

1.24

1.23

1.22

FB VOLTAGE (V)

1.21

1.20

1.19
–50

–25

3426 G07

02550

TEMPERATURE (°C)

V

OUT

500mV/DIV

I

OUT

200mA/DIV

I

L

500mA/DIV

500mV/DIV

200mA/DIV

75 100

3426 G05

Transient Response

V

OUT

250mA

= 3.3V

V

OUT

= 22µF

C

OUT

L = 2.5µH

40µs/DIVVIN = 1.8V

Switching Waveforms

V

OUT

SW

2V/DIV

I

L

= 1.8V

IN

= 3.3V

V

OUT

= 22µF

C

OUT

L = 2.5µH

500mA

3426 G08

100ns/DIVV

3426 G06

3426fa

3

LTC3426

U

UU

PI FU CTIO S

SW (Pin 1): Switch Pin. Connect inductor between SW and
V

. A Schottky diode is connected between SW and V

IN

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 100Ω antiringing
switch is connected from SW to V

to minimize EMI.

IN

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

Error Amplifier.

m

Connect resistor divider tap to this pin. The output voltage
can be adjusted from 2.5V to 5V by:

R

1

V

=+

OUT

⎛

122 1

.•

⎜
⎝

⎞
⎟

⎠

R

2

W

BLOCK DIAGRA

SHDN (Pin 4): Logic Controlled Shutdown Input.

SHDN = High: Normal free running operation

SHDN = Low: Shutdown, quiescent current < 1µA

Typically, SHDN should be connected to VIN through a 1M
pull-up resistor.

(Pin 5): Output Voltage Sense Input. The NMOS

V

OUT

switch gate drive is derived from the greater of V
V

.

IN

(Pin 6): Input Supply. Must be locally bypassed.

V

IN

OUT

and

1.22V

REFERENCE

V

OUT

SHDN

4

3

FB

R1 (EXTERNAL)

FB

R2 (EXTERNAL)

SHUTDOWN AND

SOFT-START

V

OUT

+

A1

–

R

C

C

C

GENERATOR

1.2MHz

OSCILLATOR

COMPARATOR

–

A2

+

Σ

RAMP

Figure 1

5

PWM LOGIC
AND DRIVER

V

IN

6

SW

1

+

0.02Ω

–

2

3426 F01

GND

4

3426fa