LINEAR TECHNOLOGY LTC3440 Technical data

FEATURES

LTC3440

Micropower Synchronous

Buck-Boost DC/DC Converter

U

DESCRIPTIO

■

Single Inductor

■

Fixed Frequency Operation with Battery Voltages
Above, Below or Equal to the Output

■

Synchronous Rectification: Up to 96% Efficiency

■

25µA Quiescent Current in Burst Mode® Operation

■

Up to 600mA Continuous Output Current

■

No Schottky Diodes Required (V

■

V

Disconnected from VIN During Shutdown

OUT

■

2.5V to 5.5V Input and Output Range

■

Programmable Oscillator Frequency

OUT

< 4.3V)

from 300kHz to 2MHz

■

Synchronizable Oscillator

■

Burst Mode Enable Control

■

<1µA Shutdown Current

■

Small Thermally Enhanced 10-Pin MSOP and
(3mm × 3mm) DFN Packages

U

APPLICATIO S

■

Palmtop Computers

■

Handheld Instruments

■

MP3 Players

■

Digital Cameras

The LTC®3440 is a high efficiency, fixed frequency, Buck­Boost DC/DC converter that operates from input voltages
above, below or equal to the output voltage. The topology
incorporated in the IC provides a continuous transfer
function through all operating modes, making the product
ideal for single lithium-ion, multicell alkaline or NiMH
applications where the output voltage is within the battery
voltage range.

The device includes two 0.19Ω N-channel MOSFET
switches and two 0.22Ω P-channel switches. Switching
frequencies up to 2MHz are programmed with an external
resistor and the oscillator can be synchronized to an
external clock. Quiescent current is only 25µA in Burst
Mode operation, maximizing battery life in portable appli­cations. Burst Mode operation is user controlled and can
be enabled by driving the MODE/SYNC pin high. If the
MODE/SYNC pin has either a clock or is driven low, then
fixed frequency switching is enabled.

Other features include a 1µA shutdown, soft-start con-
trol, thermal shutdown and current limit. The LTC3440 is
available in the 10-pin thermally enhanced MSOP and
(3mm × 3mm) DFN packages.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a registered trademark of Linear Technology Corporation.
Protected by U.S. Patents including 6404251, 6166527.

TYPICAL APPLICATIO

Li-Ion to 3.3V at 600mA Buck-Boost Converter

L1

10µH

3

2.7V TO 4.2V

V

IN =

+

Li-Ion

*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY

C1
10µF

*

SW1

7

V

8

SHDN/SS

2

MODE/SYNC

1

R

R

T

60.4k

IN

T

SW2

LTC3440

V

OUT

FB

V

C

GND

C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
L1: SUMIDA CDRH6D38-100

4

6

9

C5 1.5nF

10

5

U

R3

15k

R1
340k

R2
200k

C2
22µF

3440 TA01

V

OUT

3.3V
600mA

100

V

= 3.3V

OUT

98

= 100mA

I

OUT

= 1MHz

f

OSC

96

94

92

90

88

EFFICIENCY (%)

86

84

82

80

2.5

3.0

Efficiency vs V

4.0 4.5

3.5
VIN (V)

IN

5.5

5.0

3440 TA02

3440fa

1

LTC3440

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

VIN, V

SW1, SW2 Voltage ..................................... – 0.3V to 6V

VC, RT, FB, SHDN/SS,

MODE/SYNC Voltage .................................. –0.3V to 6V

Voltage........................................ –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

UU

W

PACKAGE/ORDER I FOR ATIO

TOP VIEW

R

1

T

MODE/SYNC

T

JMAX

2

3

SW1

4

SW2

5

GND

10-LEAD (3mm × 3mm) PLASTIC DFN

DD PACKAGE

EXPOSED PAD (PIN 11) IS GND

MUST BE SOLDERED TO PCB

= 125°C, θJA = 43°C/ W, θJC = 3°C/ W

10

V

C

FB

9

11

8

7

6

SHDN/SS

V

IN

V

OUT

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

range, otherwise specifications are at TA = 25°C. VIN = V

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Start-Up Voltage ● 2.4 2.5 V
Input Operating Range ● 2.5 5.5 V
Output Voltage Adjust Range ● 2.5 5.5 V

Feedback Voltage ● 1.196 1.22 1.244 V
Feedback Input Current V

Quiescent Current, Burst Mode Operation VC = 0V, MODE/SYNC = 3V (Note 3) 25 40 µA
Quiescent Current, Shutdown SHDN = 0V, Not Including Switch Leakage 0.1 1 µA

Quiescent Current, Active VC = 0V, MODE/SYNC = 0V (Note 3) 600 1000 µA
NMOS Switch Leakage Switches B and C 0.1 5 µA
PMOS Switch Leakage Switches A and D 0.1 10 µA

NMOS Switch On Resistance Switches B and C 0.19 Ω
PMOS Switch On Resistance Switches A and D 0.22 Ω

Input Current Limit ● 1A
Maximum Duty Cycle Boost (% Switch C On) ● 55 75 %

Minimum Duty Cycle ● 0%
Frequency Accuracy ● 0.8 1 1.2 MHz

MODE/SYNC Threshold 0.4 2 V
MODE/SYNC Input Current V
Error Amp AVOL 90 dB

Error Amp Source Current 15 µA
Error Amp Sink Current 380 µA

ORDER PART

NUMBER

LTC3440EDD

DD

PART MARKING

LBKT

The ● denotes specifications that apply over the full operating temperature

= 3.6V, RT = 60k, unless otherwise noted.

OUT

= 1.22V 1 50 nA

FB

Buck (% Switch A On)

MODE/SYNC

= 5.5V 0.01 1 µA

MODE/SYNC

SW1
SW2
GND

θ
θ

TOP VIEW

1

R

T

2
3
4
5

MS PACKAGE

10-LEAD PLASTIC MSOP

T

= 125°C,

JMAX

= 130°C/ W 1 LAYER BOARD

JA

= 100°C/ W 4 LAYER BOARD

JA

= 45°C/ W

θ

JC

ORDER PART

10

V
9
8
7
6

C

FB

SHDN/SS

V

IN

V

OUT

NUMBER

LTC3440EMS

MS

PART MARKING

LTNP

● 100 %

3440fa

2

LTC3440

OUTPUT CURRENT (mA)

30

EFFICIENCY (%)

90

100

20

80

50

70

60

40

0.1 10 100 1000

3440 G03

1

Burst Mode

OPERATION

VIN = 2.5V

VIN = 3.3V

f

OSC

= 2MHz

VIN = 4.2V

ELECTRICAL CHARACTERISTICS

range, otherwise specifications are at TA = 25°C. VIN = V

The ● denotes specifications that apply over the full operating temperature

= 3.6V, RT = 60k, unless otherwise noted.

OUT

PARAMETER CONDITIONS MIN TYP MAX UNITS

SHDN/SS Threshold When IC is Enabled ● 0.4 1 1.5 V

When EA is at Maximum Boost Duty Cycle 2.2 V

SHDN/SS Input Current V

Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.

Note 2: The LTC3440E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating

= 5.5V 0.01 1 µA

SHDN

temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: Current measurements are performed when the outputs are not
switching.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Li-Ion to 3.3V Efficiency
(f

= 300kHz)

OSC

100

90

Burst Mode

OPERATION

80

70

VIN = 2.5V

60

50

EFFICIENCY (%)

40

30

f

= 300kHz

OSC

20

0.1 10 100 1000

1
OUTPUT CURRENT (mA)

VIN = 4.2V

VIN = 3.3V

3440 G01

Li-Ion to 3.3V Efficiency,
Power Loss (f

100

Burst Mode

90

OPERATION

80

70

VIN = 2.5V

60

50

EFFICIENCY (%)

40

30

20

0.1 10 100 1000

1
OUTPUT CURRENT (mA)

= 1MHz)

OSC

VIN = 3.3V

VIN = 4.2V

VIN = 3.3V

f

OSC

= 1MHz

3440 G02

1000

100

POWER LOSS (mW)

10

1

0.1

Li-Ion to 3.3V Efficiency
(f

= 2MHz)

OSC

Switch Pins During Buck/Boost

SW1

2V/DIV

SW2

2V/DIV

= 3.78V 50ns/DIV 3440 G04

V

IN

V

= 3.3V

OUT

= 250mA

I

OUT

Switch Pins on the Edge of
Buck/Boost and Approaching Boost

SW1

2V/DIV

SW2

2V/DIV

= 3.42V 50ns/DIV 3440 G05

V

IN

V

= 3.3V

OUT

= 250mA

I

OUT

Switch Pins on the Edge of
Buck/Boost and Approaching Buck

SW1

2V/DIV

SW2

2V/DIV

= 4.15V 50ns/DIV 3440 G06

V

IN

V

= 3.3V

OUT

= 250mA

I

OUT

3440fa

3

LTC3440

TEMPERATURE (°C)

–55

5

E/A SOURCE CURRENT (µA)

10

15

20

–25 5 35 65

3440 G12

95 125

VIN = V

OUT

= 3.6V

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Pins in Buck Mode

Switch Pins in Boost Mode

V

Ripple During Buck,

OUT

Buck/Boost and Boost Modes

SW1

2V/DIV

SW2

2V/DIV

= 5V 250ns/DIV 3440 G07

V

IN

V

= 3.3V

OUT

I

= 250mA

OUT

SW1

2V/DIV

SW2

2V/DIV

= 2.5V 250ns/DIV 3440 G08

V

IN

V

= 3.3V

OUT

I

= 250mA

OUT

V

OUT

10mV/DIV

AC Coupled

L = 10µH1µs/DIV
C

= 22µF

OUT

I

= 250mA

OUT

f

= 1MHz

OSC

Active Quiescent Current Burst Mode Quiescent Current Error Amp Source Current

CURRENT (µA)

OUT

+ V

IN

V

550

500

450

VIN = V

OUT

= 3.6V

CURRENT (µA)

OUT

+ V

IN

V

40

VIN = V

30

20

OUT

= 3.6V

3440 G09

Buck

= 5V

V

IN

Buck/Boost

= 3.78V

V

IN

Boost
V

= 2.5V

IN

400

–55

–25 5 35 65

TEMPERATURE (°C)

95 125

3440 G10

Output Frequency NMOS R

1.10
VIN = V

1.05

1.00

FREQUENCY (MHz)

0.95

0.90

–55

= 3.6V

OUT

–25 5 35 65

TEMPERATURE (°C)

95 125

3440 G13

10

–55

0.30
VIN = V

SWITCHES B AND C

0.25

(Ω)

0.20

DS(ON)

NMOS R

0.15

0.10

–55

–25 5 35 65

TEMPERATURE (°C)

DS(ON)

= 3.6V

OUT

–25 5 35 65

TEMPERATURE (°C)

95 125

3440 G11

95 125

3440 G14

Feedback Voltage

1.236
VIN = V

1.216

FEEDBACK VOLTAGE (V)

1.196

–55

= 3V

OUT

–25 5 35 65

TEMPERATURE (°C)

95 125

3440 G15

3440fa

4

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LTC3440

Feedback Voltage Line Regulation Error Amp Sink Current PMOS R

90

VIN = V

80

70

LINE REGULATION (dB)

60

–55

= 2.5V TO 5.5V

OUT

–25 5 35 65

TEMPERATURE (°C)

95 125

3440 G16

430

VIN = V

= 3.6V

OUT

410

390

E/A SINK CURRENT (µA)

370

350

–55

–25 5 35 65

TEMPERATURE (°C)

95 125

3440 G17

0.30
VIN = V

SWITCHES A AND D

0.25

(Ω)

0.20

DS(ON)

PMOS R

0.15

0.10
–55

Boost Max Duty Cycle Minimum Start Voltage Current Limit

90

VIN = V
R

85

80

= 60k

T

OUT

= 3.6V

2.40

2.35

3000

2500

2000

DS(ON)

= 3.6V

OUT

–25 5 35 65

TEMPERATURE (°C)

VIN = V

PEAK SWITCH

95 125

= 3.6V

OUT

3440 G18

DUTY CYCLE (%)

75

70

–55

–25 5 35 65

TEMPERATURE (°C)

95 125

3440 G19

2.30

MINIMUM START VOLTAGE (V)

2.25
–55

–25 5 35 65

TEMPERATURE (°C)

95 125

3440 G20

CURRENT LIMIT (A)

1500

1000

–55

–25 5 35 65

AVERAGE INPUT

95 125

TEMPERATURE (°C)

3440 G21

3440fa

5

LTC3440

U

UU

PI FU CTIO S

RT (Pin 1): Timing Resistor to Program the Oscillator
Frequency. The programming frequency range is 300kHz
to 2MHz.

10

•

T

=

810

=

610

R

T

10

•
f

SW

Hz

f

OSC

MODE/SYNC (Pin 2): MODE/SYNC = External CLK : Syn­chronization of the internal oscillator. A clock frequency of
twice the desired switching frequency and with a pulse
width between 100ns and 2µs is applied. The oscillator
free running frequency is set slower than the desired
synchronized switching frequency to guarantee sync. The
oscillator RT component value required is given by:

R

where fSW = desired synchronized switching frequency.

SW1 (Pin 3): Switch Pin Where the Internal Switches A
and B are Connected. Connect inductor from SW1 to SW2.
An optional Schottky diode can be connected from SW1 to
ground. Minimize trace length to keep EMI down.

SW2 (Pin 4): Switch Pin Where the Internal Switches C
and D are Connected. For applications with output volt-

ages over 4.3V, a Schottky diode is required from SW2 to
V

to ensure the SW pin does not exhibit excess voltage.

OUT

GND (Pin 5): Signal and Power Ground for the IC.

(Pin 6): Output of the Synchronous Rectifier. A filter

V

OUT

capacitor is placed from V

(Pin 7): Input Supply Pin. Internal VCC for the IC. A

V

IN

ceramic bypass capacitor as close to the V
(Pin 5) is required.

SHDN/SS (Pin 8): Combined Soft-Start and Shutdown.
Grounding this pin shuts down the IC. Tie to >1.5V to
enable the IC and >2.5V to ensure the error amp is not
clamped from soft-start. An RC from the shutdown com­mand signal to this pin will provide a soft-start function by
limiting the rise time of the VC pin.

FB (Pin 9): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.5V to

5.5V. The feedback reference voltage is typically 1.22V.

VC (Pin 10): Error Amp Output. A frequency compensation
network is connected from this pin to the FB pin to
compensate the loop. See the section “Compensating the
Feedback Loop” for guidelines.

Exposed Pad (Pin 11, DFN Package Only): Ground. This
pin must be soldered to the PCB and electrically connected
to ground.

to GND.

OUT

pin and GND

IN

6

3440fa