LINEAR TECHNOLOGY LTC3441 Technical data

FEATURES

■

Regulated Output with Input Above, Below or Equal
to the Output

■

Single Inductor, No Schottky Diodes

■

High Efficiency: Up to 95%

■

25µA Quiescent Current in Burst Mode® Operation

■

Up to 1.2A Continuous Output Current from a Single
Lithium-Ion

■

True Output Disconnect in Shutdown

■

2.4V to 5.5V Input Range

■

2.4V to 5.25V Output Range

■

1MHz Fixed Frequency Operation

■

Synchronizable Oscillator

■

Selectable Burst Mode or Fixed Frequency Operation

■

<1µA Quiescent Current in Shutdown

■

Small, Thermally Enhanced 12-Lead (4mm × 3mm)
DFN package

U

APPLICATIO S

■

Handheld Computers

■

Handheld Instruments

■

MP3 Players

■

Digital Cameras

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

Burst Mode is a registered trademark of Linear Technology Corporation.

LTC3441

High Current Micropower

Synchronous Buck-Boost

DC/DC Converter

U

DESCRIPTIO

The LTC®3441 is a high efficiency, fixed frequency, buck­boost DC/DC converter that operates efficiently 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 or multicell applications where
the output voltage is within the battery voltage range.

The device includes two 0.10Ω N-channel MOSFET
switches and two 0.11Ω P-channel switches. External
Schottky diodes are optional, and can be used for a
moderate efficiency improvement. The operating frequency
is internally set to 1MHz and can be synchronized up to

1.7MHz. 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 is driven low or with a clock, then fixed fre­quency switching is enabled.

Other features include a 1µA shutdown, soft-start control,
thermal shutdown and current limit. The LTC3441 is
available in a thermally enhanced 12-lead (4mm × 3mm)
DFN package.

TYPICAL APPLICATIO

Li-Ion to 3.3V at 1A Buck-Boost Converter

L1

4.7µH

4

2.5V TO 4.2V

Li-Ion

*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY

C

IN

10µF

*

SW1

9

PV

10

V

1

SHDN/SS

7

MODE/SYNC

3

PGND

IN

IN

SW2

V

OUT

LTC3441

FB

V

C

GND

PGND

: TAIYO YUDEN JMK212BJ106MG

C

IN

: TAIYO YUDEN JMK325BJ226MM

C

OUT

L1: TOKO A916CY-4R7M

U

Efficiency vs V

100

V

= 3.3V

OUT

V

OUT

3.3V

5

8

12

15k

11

2

6

1.5nF

340k

200k

1A

C

OUT

22µF

3441 TA01

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

2.5

I

= 1A

OUT

3

3.5
VIN (V)

I

= 200mA

OUT

4 4.5

IN

5.5

5

3441 TA02

sn3441 3441fs

1

LTC3441

PACKAGE/ORDER I FOR ATIO

UU

W

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

VIN, V
SW1, SW2 Voltage

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

Pulsed < 100ns ...................................... –0.3V to 7V

SHDN/SS, MODE/SYNC Voltage ................. –0.3V to 6V

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

Maximum Junction Temperature (Note 4) ........... 125°C

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

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

OUT

TOP VIEW

13

= 125°C

12

FB

11

V

V

10

PV

9

V

8

MODE/SYNC

7

C

IN

IN

OUT

SHDN/SS

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

1

GND

2

PGND

3

SW1

4

SW2

5

PGND

6

12-LEAD (4mm × 3mm) PLASTIC DFN

DE12 PACKAGE

T

JMAX

= 53°C/W 1-LAYER BOARD

θ

JA

θ

= 43°C/W 4-LAYER BOARD

JA

= 4.3°C/W

θ

JC

EXPOSED PAD IS PGND (PIN 13)

MUST BE SOLDERED TO PCB

ORDER PART

NUMBER

LTC3441EDE

DE PART MARKING

3441

ELECTRICAL CHARACTERISTICS

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Start-Up Voltage ● 2.3 2.4 V

Output Voltage Adjust Range ● 2.4 5.25 V

Feedback Voltage ● 1.19 1.22 1.25 V

Feedback Input Current VFB = 1.22V 1 50 nA

Quiescent Current—Burst Mode Operation VC = 0V, MODE/SYNC = 3V (Note 3) 25 40 µA

Quiescent Current—SHDN V

Quiescent Current—Active MODE/SYNC = 0V (Note 3) 520 900 µA

NMOS Switch Leakage Switches B and C 0.1 7 µA

PMOS Switch Leakage Switches A and D 0.1 10 µA

NMOS Switch On Resistance Switches B and C 0.10 Ω

PMOS Switch On Resistance Switches A and D 0.11 Ω

Input Current Limit ● 2 3.2 A

Max Duty Cycle Boost (% Switch C On) ● 70 88 %

Min Duty Cycle ● 0%

Frequency Accuracy ● 0.85 1 1.15 MHz

MODE/SYNC Threshold ● 0.4 1.4 V

MODE/SYNC Input Current V

Error Amp AV

Error Amp Source Current 14 µA

Error Amp Sink Current 300 µA

SHDN/SS Threshold When IC is Enabled ● 0.4 1 1.4 V

SHDN/SS Threshold When EA is at Max Boost Duty Cycle 2 2.4 V

SHDN/SS Input Current V

OL

= SHDN = 0V, Not Including Switch Leakage 0.1 1 µA

OUT

Buck (% Switch A In)

MODE/SYNC

SHDN

= 5.5V 0.01 1 µA

= 5.5V 0.01 1 µA

The ● denotes the specifications which apply over the full operating

= 3.6V,unless otherwise noted.

OUT

● 100 %

90 dB

sn3441 3441fs

2

ELECTRICAL CHARACTERISTICS

LTC3441

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

Note 2: The LTC3441E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation

Note 4: 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 result in device degradation or failure.

with statistical process controls.
Note 3: Current measurements are preformed when the outputs are not

switching.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Efficiency

100

90

Burst Mode

OPERATION

80

70

60

50

VIN = 2.7V

40

EFFICIENCY (%)

30

20

10

V

= 3.3V

OUT

0

0.1 10 100 1000

1

I

OUT

VIN = 4.2V

VIN = 3.6V

(mA)

3441 G17

10mV/DIV

AC-COUPLED

V

Ripple at 1A Load

OUT

V

OUT

L = 4.7µH1µs/DIV
C

= 47µF

OUT

I

= 1A

OUT

= 3.3V

V

OUT

3441 G02

BUCK
VIN = 4.2V

BUCK-BOOST
V

= 3.3V

IN

BOOST
V

= 2.7V

IN

V

OUT

100mV/DIV

1A

100mA

Load Transient Response,
100mA to 1A

100µs/DIV

3441 G01

Switch Pins in Buck-Boost Mode

SW1

2V/DIV

SW2

2V/DIV

V

= 3.3V 50ns/DIV 3441 G03

IN

V

= 3.3V

OUT

I

= 500mA

OUT

Switch Pins Entering
Buck-Boost Mode

SW1

2V/DIV

SW2

2V/DIV

V

= 4.2V 50ns/DIV 3441 G04

IN

V

= 3.3V

OUT

I

= 500mA

OUT

sn3441 3441fs

3

LTC3441

TEMPERATURE (°C)

–55

2.8

CURRENT LIMIT (A)

3.0

3.2

3.4

–25 5 35 65

3441 G13

95

125

VIN = V

OUT

= 3.6V

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Pins Before Entering

Active Quiescent Current

630

CURRENT (µA)

OUT

+ V

IN

V

620

610

600

590

580

570

560

550

540

530

520

VIN = V

–55

= 3.6V

OUT

–25 5 35 65

TEMPERATURE (°C)

95 125

SW1

2V/DIV

SW2

2V/DIV

Boost Mode

= 3V 50ns/DIV 3441 G05

V

IN

V

= 3.3V

OUT

= 500mA

I

OUT

3441 G06

Feedback Voltage

1.241
VIN = V

= 3.6V

–55

OUT

–25

TEMPERATURE (°C)

1.236

1.231

1.226

1.221

1.216

1.211

FEEDBACK VOLTAGE (V)

1.206

1.201

1.196

5

35 125

65

95

3441 G07

Burst Mode Quiescent Current

50

CURRENT (µA)

OUT

+ V

IN

V

VIN = V

40

30

20

10

–55

= 3.6V

OUT

–25 5 35 65

TEMPERATURE (°C)

Error Amp Sink Current

400

VIN = V

350

300

OUT

= 3.6V

95 125

3441 G08

Feedback Voltage Line Regulation Error Amp Source Current

90

VIN = V

80

70

LINE REGULATION (dB)

60

–55

= 2.4V TO 5.5V

OUT

–25 5 35 65

TEMPERATURE (°C)

125

95

3441 G09

20

VIN = V

= 3.6V

OUT

15

10

EA SOURCE CURRENT (µA)

5

–55

–25 5 35 65

TEMPERATURE (°C)

Output Frequency Current Limit

1.2
VIN = V

1.1

1.0

OUT

= 3.6V

125

95

3441 G10

EA SINK CURRENT (µA)

250

200

4

–55

–25 5 35 65

TEMPERATURE (°C)

95 125

3441 G11

FREQUENCY (MHz)

0.9

0.8
–55

–25 5 35 65

TEMPERATURE (°C)

95 125

3441 G12

sn3441 3441fs

UW

TEMPERATURE (°C)

–55

2.10

MINIMUM START VOLTAGE (V)

2.15

2.20

2.25

2.30

–25 5 35 65

3441 G16

95 125

TYPICAL PERFOR A CE CHARACTERISTICS

LTC3441

NMOS R

0.15
VIN = V
SWITCHES B AND C

0.13

(Ω)

0.11

DS(ON)

0.09

NMOS R

0.07

0.05

–55

U

DS(ON)

= 3.6V

OUT

53565

–25

TEMPERATURE (°C)

95 125

3441 G14

UU

0.15

0.14

0.13

0.12

(Ω)

0.11

0.10

DS(ON)

0.09

PMOS R

0.08

0.07

0.06

0.05

PMOS R

–50

DS(ON)

VIN = V
SWITCHES A AND D

= 3.6V

OUT

–25

5

TEMPERATURE (°C)

PI FU CTIO S

SHDN/SS (Pin 1): Combined Soft-Start and Shutdown.
Applied voltage < 0.4V shuts down the IC. Tie to >1.4V to
enable the IC and >2.4V 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.

GND (Pin 2): Signal Ground for the IC.

PGND (Pins 3, 6, 13 Exposed Pad): Power Ground for the

Internal NMOS Power Switches

Minimum Start Voltage

35 65

125

95

3441 G15

light loads. The Burst Mode operation will continue until
the pin is driven low.

MODE/SYNC = Low: Disable Burst Mode operation and
maintain low noise, constant frequency operation .

MODE/SYNC = External CLK : Synchronization of the
internal oscillator and Burst Mode operation disable. A
clock pulse width between 100ns and 2µs and a clock
frequency between 2.3MHz and 3.4MHz (twice the
desired frequency) is required to synchronize the IC.

SW1 (Pin 4): 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 this SW1
to ground. Minimize trace length to keep EMI down.

SW2 (Pin 5): Switch pin where the internal switches C
and D are connected. An optional Schottky diode can be
connected from SW2 to V
V

> 4.3V). Minimize trace length to keep EMI down.

OUT

MODE/SYNC (Pin 7): Burst Mode Select and Oscillator
Synchronization.

MODE/SYNC = High: Enable Burst Mode Operation.
During the period where the IC is supplying energy to
the output, the inductor peak inductor current will reach

0.8A and return to zero current on each cycle. In Burst
Mode operation the operation is variable frequency,
which provides a significant efficiency improvement at

(it is required where

OUT

f

= f

OSC

V

(Pin 8): Output of the Synchronous Rectifier. A filter

OUT

capacitor is placed from V
capacitor is recommended as close to the V

SYNC

/2

to GND. A ceramic bypass

OUT

and GND

OUT

pins as possible.

PVIN (Pin 9): Power VIN Supply Pin. A 10µF ceramic capaci-
tor is recommended as close to the PVIN and PGND pins
as possible

VIN (Pin 10): Input Supply Pin. Internal VCC for the IC.

VC (Pin 11): 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.

FB (Pin 12): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.4V to

5.25V. The feedback reference voltage is typically 1.22V.

sn3441 3441fs

5

LTC3441

BLOCK DIAGRA

W

2.4V TO 5.5V

+

V

IN

PV

IN

9

V

IN

10

SW A

3.2A

+

4A

–

V

CC

INTERNAL

+

2.4V

–

4 5

SW1

SW B

ANTICROSS

CONDUCTION

+

1

= k

g

m

100

–

AVERAGE

CURRENT LIMIT

SUPPLY

CURRENT

LIMIT

UVLO

GATE

DRIVERS

AND

PWM

LOGIC

AND

OUTPUT

PHASING

SW2

SW C

I

SENSE

AMP

PGND

THERMAL

SHUTDOWN

PWM

COMPARATORS

–0.8A

–

–

+

–

+

SW D

+

REVERSE
CURRENT

LIMIT

ERROR

AMP

CLAMP

V

OUT

8

1.22V

+

FB

–

12

V

OUT

2.4V TO 5.25V

R1

MODE/SYNC

7

1 = Burst Mode
OPERATION
0 = FIXED FREQUENCY

1MHz

OSC

SYNC

÷2

SLEEP

Burst Mode

OPERATION

CONTROL

5µs DELAY

GND

2

V

C

11

R2

R

SHUTDOWN

PGND

6

SHDN/SS

SS

1

V

IN

C

SS

3440 BD

6

sn3441 3441fs

OPERATIO

75%

D

MAX

BOOST

D

MIN

BOOST

D

MAX

BUCK

DUTY

CYCLE

0%

V4 (≈2.05V)

V3 (≈1.65V)

BOOST REGION

BUCK REGION

BUCK/BOOST REGION

V2 (≈1.55V)

V1 (≈0.9V)

3441 F02

A ON, B OFF

PWM CD SWITCHES

D ON, C OFF

PWM AB SWITCHES

FOUR SWITCH PWM

INTERNAL
CONTROL
VOLTAGE, V

CI

LTC3441

U

The LTC3441 provides high efficiency, low noise power for
applications such as portable instrumentation. The LTC
proprietary topology allows input voltages above, below or
equal to the output voltage by properly phasing the output
switches. The error amp output voltage on the VC pin de­termines the output duty cycle of the switches. Since the
VC pin is a filtered signal, it provides rejection of frequen­cies from well below the switching frequency. The low
R

, low gate charge synchronous switches provide

DS(ON)

high frequency pulse width modulation control at high
efficiency. Schottky diodes across the synchronous switch
D and synchronous switch B are not required, but provide
a lower drop during the break-before-make time (typically
15ns). The addition of the Schottky diodes will improve peak
efficiency by typically 1% to 2%. High efficiency is achieved
at light loads when Burst Mode operation is entered and
when the IC’s quiescent current is a low 25µA.

LOW NOISE FIXED FREQUENCY OPERATION

Oscillator

The frequency of operation is factory trimmed to 1MHz.
The oscillator can be synchronized with an external clock
applied to the MODE/SYNC pin. A clock frequency of twice
the desired switching frequency and with a pulse width of
at least 100ns is applied. The oscillator sync range is

1.15MHz to 1.7MHz (2.3MHz to 3.4MHz sync frequency).

Error Amp

The error amplifier is a voltage mode amplifier. The loop
compensation components are configured around the
amplifier to obtain stability of the converter. The SHDN/SS
pin will clamp the error amp output, V

, to provide a soft-

C

start function.

Reverse Current Limit

The reverse current limit amplifier monitors the inductor
current from the output through switch D. Once a negative
inductor current exceeds –800mA typical, the IC will shut
off switch D.

Output Switch Control

Figure 1 shows a simplified diagram of how the four
internal switches are connected to the inductor, VIN, V

OUT

and GND. Figure 2 shows the regions of operation for the
LTC3441 as a function of the internal control voltage, V

.

CI

The VCI voltage is a level shifted voltage from the output of
the error amp (VC pin) (see Figure 5). The output switches
are properly phased so the transfer between operation
modes is continuous, filtered and transparent to the user.
When VIN approaches V

the Buck/Boost region is

OUT

reached where the conduction time of the four switch
region is typically 150ns. Referring to Figures 1 and 2, the
various regions of operation will now be described.

PV

IN

9

PMOS A

SW1

4

NMOS B

Figure 1. Simplified Diagram of Output Switches

SW2

5

V

OUT

V

8

OUT

PMOS D

NMOS C

3441 F01

Supply Current Limit

The current limit amplifier will shut PMOS switch A off
once the current exceeds 4A typical. Before the switch
current limit, the average current limit amp (3.2A typical)
will source current into the FB pin to drop the output
voltage. The current amplifier delay to output is typically
50ns.

Figure 2. Switch Control vs Internal Control Voltage, V

CI

sn3441 3441fs

7

LTC3441

OPERATIO

U

Buck Region (VIN > V

OUT

)

Switch D is always on and switch C is always off during this
mode. When the internal control voltage, V

, is above

CI

voltage V1, output A begins to switch. During the off time
of switch A, synchronous switch B turns on for the
remainder of the time. Switches A and B will alternate
similar to a typical synchronous buck regulator. As the
control voltage increases, the duty cycle of switch A
increases until the maximum duty cycle of the converter in
Buck mode reaches D

D

MAX_BUCK

= 100 – D4SW %

MAX_BUCK

, given by:

where D4SW = duty cycle % of the four switch range.

D4SW = (150ns • f) • 100 %

where f = operating frequency, Hz.

Beyond this point the “four switch,” or Buck/Boost region
is reached.

Buck/Boost or Four Switch (VIN ~ V

OUT

)

When the internal control voltage, VCI, is above voltage V2,
switch pair AD remain on for duty cycle D

MAX_BUCK

, and
the switch pair AC begins to phase in. As switch pair AC
phases in, switch pair BD phases out accordingly. When
the VCI voltage reaches the edge of the Buck/Boost range,
at voltage V3, the AC switch pair completely phase out the
BD pair, and the boost phase begins at duty cycle D4SW.

The input voltage, VIN, where the four switch region begins
is given by:

V

V

=

IN

OUT

1 150–( • )

ns f

V

The point at which the four switch region ends is given by:

voltage V3, switch pair CD will alternately switch to
provide a boosted output voltage. This operation is typical
to a synchronous boost regulator. The maximum duty
cycle of the converter is limited to 88% typical and is
reached when VCI is above V4.

Burst Mode OPERATION

Burst Mode operation is when the IC delivers energy to the
output until it is regulated and then goes into a sleep mode
where the outputs are off and the IC is consuming only
25µA. In this mode the output ripple has a variable
frequency component that depends upon load current.

During the period where the device is delivering energy to
the output, the peak current will be equal to 800mA typical
and the inductor current will terminate at zero current for
each cycle. In this mode the typical maximum average
output current is given by:

V

.•

02

I

OUT MAX BURST

()

≈

VV

IN

+

OUT IN

A

Burst Mode operation is user controlled, by driving the
MODE/SYNC pin high to enable and low to disable.

The peak efficiency during Burst Mode operation is less
than the peak efficiency during fixed frequency because
the part enters full-time 4-switch mode (when servicing
the output) with discontinuous inductor current as illus­trated in Figures 3 and 4. During Burst Mode operation, the
control loop is nonlinear and cannot utilize the control
voltage from the error amp to determine the control mode,
therefore full-time 4-switch mode is required to maintain
the Buck/Boost function. The efficiency below 1mA
becomes dominated primarily by the quiescent current
and not the peak efficiency. The equation is given by:

VIN = V

Boost Region (VIN < V

(1 – D) = V

OUT

(1 – 150ns • f) V

OUT

)

OUT

Switch A is always on and switch B is always off during
this mode. When the internal control voltage, VCI, is above

8

Efficiency Burst

η

≈

25 A I

µ+

LOAD

LOAD

( bm) • I

where (ηbm) is typically 75% during Burst Mode
operation

.

sn3441 3441fs

OPERATIO

LTC3441

U

Burst Mode Operation to Fixed Frequency Transient
Response

When transitioning from Burst Mode operation to fixed
frequency, the system exhibits a transient since the modes
of operation have changed. For most systems this tran­sient is acceptable, but the application may have stringent
input current and/or output voltage requirements that
dictate a broad-band voltage loop to minimize the tran-

SOFT-START

The soft-start function is combined with shutdown. When
the SHDN/SS pin is brought above typically 1V, the IC is
enabled but the EA duty cycle is clamped from the VC pin.
A detailed diagram of this function is shown in Figure 5.
The components R

and CSS provide a slow ramping

SS

voltage on the SHDN/SS pin to provide a soft-start

function.
sient. Lowering the DC gain of the loop will facilitate the
task (5M from FB to VC) at the expense of DC load
regulation. Type 3 compensation is also recommended to
broad band the loop and roll off past the two pole response
of the LC of the converter (see Closing the Feedback Loop).

PV

IN

9

V

dI

A

4

SW1

B

IN

≈

L

dt

+–

L

6

GND

Figure 3. Inductor Charge Cycle During Burst Mode Operation Figure 4. Inductor Discharge Cycle During Burst Mode Operation

5

SW2

V

OUT

8

D

800mA

INDUCTOR

C

I

0mA

T1

3441 F03

PV

IN

9

V

dI

A

4

SW1

B

OUT

≈ –

L

dt

–+

L

6

GND

5

SW2

V

OUT

8

D

800mA

INDUCTOR

C

I

0mA

T2

3441 F04

TO PWM

COMPARATORS

V

CI

V

IN

SOFT-START

CLAMP

ERROR AMP

14µA

+

–

+

CHIP

ENABLE

–

Figure 5. Soft-Start Circuitry

1.22V

1V

FB

12

V

C

11

SHDN/SS

1

V

OUT

R1

C

P1

R2

R

SS

ENABLE SIGNAL

C

SS

3441 F05

sn3441 3441fs

9

LTC3441

WUUU

APPLICATIO S I FOR ATIO

COMPONENT SELECTION

V

PV

V

OUT

MODE

FB

V

IN

IN

12

11

C

10

9

8

7

MULTIPLE VIAS

V

IN

V

OUT

3441 F06

and V

OUT

IN

SHDN/SS

1

GND

2

PGND

3

SW1

4

SW2

5

PGND

6

GND

Figure 6. Recommended Component Placement. Traces Carrying
High Current are Direct. Trace Area at FB and VC Pins are Kept
Low. Lead Length to Battery Should be Kept Short. V
Ceramic Capacitors Close to the IC Pins

Inductor Selection

The high frequency operation of the LTC3441 allows the
use of small surface mount inductors. The inductor cur­rent ripple is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:

VVV

L

>

L

>

f I Ripple V

2

•– •

IN MIN OUT IN MIN

() ()

f I Ripple V

••%•

VV V

OUT IN MAX OUT

••%•

OUT MAX IN MAX

()

OUT MAX OUT

()

•–•

()

()

() ()

100

2

100

H

,

H

where f = operating frequency, Hz
%Ripple = allowable inductor current ripple, %
V
V
V
I

OUT(MAX)

= minimum input voltage, V

IN(MIN)

IN(MAX)

OUT

= maximum input voltage, V

= output voltage, V

= maximum output load current

For high efficiency, choose an inductor with a high fre­quency core material, such as ferrite, to reduce core loses.
The inductor should have low ESR (equivalent series
resistance) to reduce the I2R losses, and must be able to

handle the peak inductor current without saturating. Molded

chokes or chip inductors usually do not have enough core

to support the peak inductor currents in the 1A to 2A

region. To minimize radiated noise, use a toroid, pot core

or shielded bobbin inductor. See Table 1 for suggested

components and Table 2 for a list of component suppliers.

Table 1. Inductor Vendor Information

SUPPLIER PHONE FAX WEB SITE

Coilcraft [phone] [phone] www.coilcraft.com

Coiltronics [phone] [phone] www.coiltronics.com

Murata USA: USA: www.murata.com

[phone] [phone]
[phone]

Sumida USA: www.japanlink.com/

[phone] [phone] sumida
Japan:
81(3) 3607-5111 81(3) 3607-5144

Output Capacitor Selection

The bulk value of the capacitor is set to reduce the ripple

due to charge into the capacitor each cycle. The steady

state ripple due to charge is given by:

%_

Ripple Boost

Ripple Buck

%_

where C

= output filter capacitor, F

OUT

IVV

OUT MAX OUT IN MIN

=

IVV

() ()

OUT MAX IN MAX OUT

=

•– •

() ()

CV Vf

()

2

••

CV f

OUT OUT

•–•

()

•••

OUT IN MAX OUT

()

100

%

100

%

The output capacitance is usually many times larger in

order to handle the transient response of the converter.

For a rule of thumb, the ratio of the operating frequency to

the unity-gain bandwidth of the converter is the amount

the output capacitance will have to increase from the

above calculations in order to maintain the desired tran-

sient response.

The other component of ripple is due to the ESR (equiva-

lent series resistance) of the output capacitor. Low ESR

capacitors should be used to minimize output voltage

ripple. For surface mount applications, Taiyo Yuden ce-

ramic capacitors, AVX TPS series tantalum capacitors or

Sanyo POSCAP are recommended.

10

sn3441 3441fs

WUUU

APPLICATIO S I FOR ATIO

LTC3441

Input Capacitor Selection

Since the VIN pin is the supply voltage for the IC it is
recommended to place at least a 4.7µF, low ESR bypass
capacitor.

Table 2. Capacitor Vendor Information

SUPPLIER PHONE FAX WEB SITE

AVX [phone] [phone] www.avxcorp.com

Sanyo [phone] [phone] www.sanyovideo.com

Taiyo Yuden [phone] [phone] www.t-yuden.com

Optional Schottky Diodes

The Schottky diodes across the synchronous switches B
and D are not required (V

< 4.3V), but provide a lower

OUT

drop during the break-before-make time (typically 15ns)
of the NMOS to PMOS transition, improving efficiency.
Use a Schottky diode such as an MBRM120T3 or equiva­lent. Do not use ordinary rectifier diodes, since the slow
recovery times will compromise efficiency. For applica­tions with an output voltage above 4.3V, a Schottky diode
is required from SW2 to V

OUT

.

Output Voltage < 2.4V

The LTC3441 can operate as a buck converter with output
voltages as low as 0.4V. The part is specified at 2.4V
minimum to allow operation without the requirement of a
Schottky diode. Synchronous switch D is powered from
V

and the R

OUT

therefore a Schottky diode is required from SW2 to V

will increase at low output voltages,

DS(ON)

OUT

to provide the conduction path to the output.

Output Voltage > 4.3V

input voltages, VIN bypassing becomes more critical;

therefore, a ceramic bypass capacitor as close to the V

IN

and GND pins as possible is also required.

Operating Frequency Selection

Additional quiescent current due to the output switches

GATE charge is given by:

Buck: 800e

Boost: 400e

Buck/Boost: f • (1200e

–12

• VIN • f

–12

• (VIN + V

) • f

OUT

–12

• VIN + 400e

–12

• V

OUT

)

where f = switching frequency

Closing the Feedback Loop

The LTC3441 incorporates voltage mode PWM control.

The control to output gain varies with operation region

(Buck, Boost, Buck/Boost), but is usually no greater than

15. The output filter exhibits a double pole response is

given by:

f

FILTER POLE

where C

=

_

is the output filter capacitor.

OUT

2

1

•• •

π

LC

Hz

OUT

The output filter zero is given by:

f

FILTER ZERO

where R

_

ESR

=

•• •

2

is the capacitor equivalent series resistance.

1

RC

π

ESR OUT

Hz

A troublesome feature in Boost mode is the right-half

plane zero (RHP), and is given by:

A Schottky diode from SW to V

is required for output

OUT

voltages over 4.3V. The diode must be located as close to
the pins as possible in order to reduce the peak voltage on
SW2 due to the parasitic lead and trace inductance.

Input Voltage > 4.5V

For applications with input voltages above 4.5V which
could exhibit an overload or short-circuit condition, a
2Ω/1nF series snubber is required between the SW1 pin
and GND. A Schottky diode from SW1 to VIN should also
be added as close to the pins as possible. For the higher

2

V

f

RHPZ

=

2• • • •

IN

ILV

π

OUT OUT

Hz

The loop gain is typically rolled off before the RHP zero

frequency.

A simple Type I compensation network can be incorpo-

rated to stabilize the loop but at a cost of reduced band-

width and slower transient response. To ensure proper

phase margin, the loop requires to be crossed over a

decade before the LC double pole.

sn3441 3441fs

11

LTC3441

WUUU

APPLICATIO S I FOR ATIO

The unity-gain frequency of the error amplifier with the
Type I compensation is given by:

f

UG

=

211•• •

1

RCP

π

Hz

Most applications demand an improved transient response
to allow a smaller output filter capacitor. To achieve a
higher bandwidth, Type III compensation is required. Two
zeros are required to compensate for the double-pole
response.

f

POLE

≈

1

π

•• • •

232 1

1

3

eRC

P

Hz

1

Which is extremely close toDC

f

ZERO

f

ZERO

f

POLE

=

1

2

=

2

=

2

1

π

•• •

RC

ZP

1

1

21

π

•• •

RC

Z

1

1

2

π

•• •

RC

ZP

Hz

Hz

Hz

2

V

OUT

1.22V

+

ERROR

AMP

FB

12

–

C

P1

V

C

11

R1

R2

3441 F07

Figure 7. Error Amplifier with Type I Compensation

V

OUT

1.22V

ERROR

AMP

+

FB

12

–

C

V

C

11

P1

R

Z

C

P2

3441 F08

C

R1

R2

Z1

Figure 8. Error Amplifier with Type III Compensation

2.5V TO 4.2V

Li-Ion

*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY

C1
10µF

*

4

SW1

9

PV

10

V

1

SHDN/SS

7

MODE/SYNC

3

PGND

L1

IN

IN

4.7µH

5

SW2

8

V

OUT

LTC3441

12

FB

11

V

C

2

GND

6

PGND

C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ476MM
L1: TOKO A916CY-4R7M

R3 15k

C4 220pF

5M

R1
348k

R2
200k

220pF

2.2k

V

3.3V
1A

C2
47µF

3441 F09

OUT

V

OUT

100mV/DIV

1A

100mA

Figure 9. Fast Transient Response Compensation for Step Load or Mode Change

Load Transient Response,

100mA to 1A

100µs/DIV 3441 G01

sn3441 3441fs

12

TYPICAL APPLICATIO S

LTC3441

U

Li-Ion to 3.3V at 1.2A Converter

2.8V TO 4.2V

Li-Ion

*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY

D2

*

C1
10µF

100

90

4.2V

80

70

60

2.8V

50

40

EFFICIENCY (%)

30

20

10

0

0.1

L1

4.7µH

4

SW1

9

PV

10

V

1

SHDN/SS

7

MODE/SYNC

3

PGND

IN

IN

SW2

V

OUT

LTC3441

FB

V

C

GND

PGND

C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
D1, D2: ON SEMICONDUCTOR MBRM120LT3
L1: TOKO A916CY-3R3M

Efficiency

BURST

IN

PWM

IN

1 10 10000100 1000

3.6V

I

OUT

IN

(mA)

4.2V

PWM

IN

5

8

12

11

2

6

PWM

D1

R3 15k

3441 TA03b

C4 1.5nF

R1
340k

R2
200k

V

OUT

3.3V

1.2A

C2
22µF

3441 TA03a

sn3441 3441fs

13

LTC3441

TYPICAL APPLICATIO S

Li-Ion to 5V at 600mA Boost Converter with Output Disconnect

U

2.5V TO 4.2V

Li-Ion

0.047µF

*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY

L1

4.7µH

4

1M

C1
10µF

*

SW1

9

PV

10

V

1

SHDN/SS

7

MODE/SYNC

3

PGND

IN

IN

SW2

V

OUT

LTC3441

C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
D1: MBRM120LT3
L1: TOKO A916CY-4R7M

GND

PGND

FB

V

C

Efficiency

100

90

Burst Mode

80

OPERATION

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 10 100 1000

VIN = 4.2V

VIN = 3.6 V

1

OUTPUT CURRENT (mA)

5

8

12

11

2

6

VIN = 2.7V

3441 TA04b

D1

R3 15k

C4 1.5nF

R1
619k

R2
200k

V

OUT

5V
600mA

C

OUT

22µF

3441 TA04a

14

sn3441 3441fs

PACKAGE DESCRIPTIO

LTC3441

U

DE/UE Package

12-Lead Plastic DFN (4mm × 3mm)

(Reference LTC DWG # 05-08-1695)

0.65 ±0.05

3.50 ±0.05

1.70 ±0.05
(2 SIDES)2.20 ±0.05

PACKAGE OUTLINE

0.25 ± 0.05

3.30 ±0.05
(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

4.00 ±0.10
(2 SIDES)

PIN 1

TOP MARK

(NOTE 6)

0.200 REF

NOTE:

1. DRAWING PROPOSED TO BE A VARIATION OF VERSION
(WGED) IN JEDEC PACKAGE OUTLINE M0-229

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION

ON THE TOP AND BOTTOM OF PACKAGE

0.50
BSC

3.00 ±0.10
(2 SIDES)

0.75 ±0.05

R = 0.20

TYP

1.70 ± 0.10
(2 SIDES)

0.00 – 0.05

R = 0.115

TYP

0.25 ± 0.05

3.30 ±0.10
(2 SIDES)

BOTTOM VIEW—EXPOSED PAD

0.50
BSC

127

16

0.38 ± 0.10

PIN 1
NOTCH

(UE12/DE12) DFN 0603

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.

sn3441 3441fs

15

LTC3441

TYPICAL APPLICATIO

R

S

V

0.05Ω

IN

2.5V TO 5.5V
1A MAX

R4

1k

AVERAGE INPUT

CURRENT CONTROL

RELATED PARTS

U

C1
10µF

+

1/2 LT1490A

–

PCMCIA Powered GSM Modem

L1

10µH

4

9

10

1

7

3

SW1

PV

IN

LTC3441

V

IN

SHDN/SS

MODE/SYNC

PGND

2N3906

I

SW2

V

OUT

FB

V

C

GND

PGND

CURRENTLIMIT

5

8

12

11

2

6

=

1.22 • R4
R5 • R

10nF

S

R6

24k

C4

1N914

+

1/2 LT1490A

–

R5
24k

C1: TAIYO YUDEN JMK212BJ106MG
C2: SANYO MV-AX SERIES
L1: TOKO A916CY-4R7M

R1
392k

R2
200k

V

OUT

3.6V
2A (PULSED)

C

OUT

2200µF

3441 TA05

PART NUMBER DESCRIPTION COMMENTS

LT®1613 550mA (ISW) 1.4MHz High Efficiency Step-Up DC/DC Converter VIN: 0.9V to 10V, V

: ≤ 1µA, ThinSOT

I

SD

LT1615/LT1615-1 300mA/80mA (ISW) Constant Off-Time, High Efficiency Step-Up VIN: 1.2V to 15V, V

DC/DC Converter I

LT1616 500mA (I

LTC1776 500mA (I

LTC1877 600mA (I

LTC1878 600mA (I

LTC1879 1.2A (I

OUT

) 1.4MHz High Efficiency Step-Down DC/DC Converter High Efficiency, VIN: 3.6V to 25V, V

OUT

) 200kHz High Efficiency Step-Down DC/DC Converter High Efficiency, VIN: 7.4V to 40V, V

OUT

) 550kHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 10V, V

OUT

) 550kHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 6V, V

OUT

) 550kHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 10V, V

: ≤ 1µA, ThinSOT

SD

I

: ≤ 1µA, ThinSOT

SD

: 30µA, N8, S8

I

SD

: ≤ 1µA, MS8

I

SD

I

: ≤ 1µA, MS8

SD

I

: ≤ 1µA, TSSOP16

SD

LT1930/LT1930A 1A (ISW) 1.2MHz/2.2MHz High Efficiency Step-Up DC/DC Converter VIN: 2.6V to 16V, V

: ≤ 1µA, ThinSOT

I

SD

LTC3405/LTC3405A 300mA (I

LTC3406/LTC3406B 600mA (I

LTC3407 600mA (I

DC/DC Converter I

LTC3411 1.25A (I

LTC3412 2.5A (I

LTC3440 600mA (I

) 1.5MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.7V to 6V, V

OUT

) 1.5MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, V

OUT

) ×2 1.5MHz Dual Synchronous Step-Down 96% Efficiency, VIN: 2.5V to 5.5V, V

OUT

) 4MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, V

OUT

) 4MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, V

OUT

) 2MHz Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, V

OUT

: ≤ 1µA, ThinSOT

I

SD

I

: ≤ 1µA, ThinSOT

SD

: ≤ 1µA, 10-Lead MS

SD

: ≤ 1µA, 10-Lead MS

I

SD

: ≤ 1µA, TSSOP16E

I

SD

I

: ≤ 1µA, 10-Lead MS

SD

ThinSOT is a trademark of Linear Technology Corporation.

Linear Technology Corporation

16

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear.com

: 34V, IQ: 3mA,

OUT(MAX)

TM

: 34V, IQ: 20µA,

OUT(MAX)

: 1.25V, IQ: 1.9mA,

OUT(MIN)

: 1.24V, IQ: 3.2mA,

OUT(MIN)

: 0.8V, IQ: 10µA,

OUT(MIN)

: 0.8V, IQ: 10µA,

OUT(MIN)

: 0.8V, IQ: 15µA,

OUT(MIN)

: 34V, IQ: 5.5mA,

OUT(MAX)

: 0.8V, IQ: 20µA,

OUT(MIN)

: 0.6V, IQ: 20µA,

OUT(MIN)

: 0.6V, IQ: 40µA,

OUT(MIN)

: 0.8V, IQ: 60µA,

OUT(MIN)

: 0.8V, IQ: 60µA,

OUT(MIN)

: 2.5V, IQ: 25µA,

OUT(MIN)

LT/TP 0703 1K • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2003

sn3441 3441fs