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LT1944-1

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

Dual Micropower Step-Up

DC/DC Converter

The LT

1944-1 is a dual micropower step-up DC/DC

converter in a 10-pin MSOP package. One converter is

designed with a 100mA current limit and a 400ns off-time;

the other with a 175mA current limit and a 1.5µs off-time.

The 1.5µs off-time converter is ideal for generating an

output voltage that is close to the input voltage (i.e. a Li-

Ion to 5V converter, or a two-cell to 3.3V converter). With

an input voltage range of 1.2V to 15V, the LT1944-1 is ideal

for a wide variety of applications. Both converters feature

a quiescent current of only 20µA at no load, which further

reduces to 0.5µA in shutdown. A current limited, fixed off-

time control scheme conserves operating current, result-

ing in high efficiency over a broad range of load current.

Tiny, low profile inductors and capacitors can be used to

minimize footprint and cost in space-conscious portable

applications.

■

Low Quiescent Current:

A in Active Mode

A in Shutdown Mode

■

Operates with V

as Low as 1.2V

■

Low V

CESAT

Switches: 85mV at 70mA

■

Uses Small Surface Mount Components

■

High Output Voltage: Up to 34V

■

Tiny 10-Pin MSOP Package

■

Small TFT LCD Panels

■

Handheld Computers

■

Battery Backup

■

Digital Cameras

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

SW2

FB1

LT1944-1

22µHD1

SHDN1 324k

4.7µF

40mA

15V

2.5mA

–10V

1mA

2.7V

TO 4.2V

1944-1 TA01

GND

PGND

SW1

4.7pF

4.7µF

FB2

SHDN2

22µHD2

178k

1µF

4.7pF

C1, C2: TAIYO YUDEN JMK212BJ475

C3, C4: TAIYO YUDEN EMK212BJ105

C5: TAIYO YUDEN EMK107BJ104

D1, D2, D3, D4: CENTRAL SEMI CMDSH3

L1, L2: MURATA LQH3C220

0.1µF

1µF

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

1 10 100

1944-1 TA01a

= 4.2V

= 2.7V

Triple Output Power Supply (5V, 15V, –10V) for LCD Displays

5V Output Efficiency

LT1944-1

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

UUW

(Note 1)

, SHDN1, SHDN2 Voltage ................................... 15V

SW1, SW2 Voltage .................................................. 36V

FB1, FB2 Voltage .......................................................V

Current into FB1, FB2 Pins ..................................... 1mA

Junction Temperature...........................................125°C

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

Storage Temperature Range ................. –65°C to 150°C

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

ORDER PART

NUMBER

LT1944-1EMS

MS10 PART

MARKING

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage 1.2 V

Quiescent Current, Each Switcher Not Switching 20 30 µA

SHDN

= 0V 1µA

FB Comparator Trip Point ●1.205 1.23 1.255 V

FB Comparator Hysteresis 8mV

FB Voltage Line Regulation 1.2V < V

< 12V 0.05 0.1 %/V

FB Pin Bias Current (Note 3) V

= 1.23V ●30 80 nA

Switch Off Time, Switcher 1 (Note 4) V

> 1V 400 ns

< 0.6V 1.5 µs

Switch Off Time, Switcher 2 (Note 4) V

> 1V 1.5 µs

< 0.6V 1.5 µs

Switch V

CESAT

= 70mA 85 120 mV

Switch Current Limit, Switcher 1 65 100 125 mA

Switch Current Limit, Switcher 2 130 175 225 mA

SHDN Pin Current V

SHDN

= 1.2V 2 3 µA

SHDN

= 5V 8 12 µA

SHDN Input Voltage High 0.9 V

SHDN Input Voltage Low 0.25 V

Switch Leakage Current Switch Off, V

= 5V 0.01 5 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 2: The LT1944-1E is guaranteed to meet performance specifications

from 0°C to 70°C. Specifications over the –40°C to 85°C operating

JMAX

= 125°C, θ

= 160°C/W

temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted.

LTTU

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

FB1

SHDN1

GND

SHDN2

FB2

SW1

PGND

VIN

PGND

SW2

TOP VIEW

MS10 PACKAGE

10-LEAD PLASTIC MSOP

temperature range are assured by design, characterization and correlation

with statistical process controls.

Note 3: Bias current flows into the FB pin.

Note 4: See Figure 1 for Switcher 1 and Switcher 2 locations.

LT1944-1

TYPICAL PERFOR A CE CHARACTERISTICS

Switch Saturation Voltage

(VCESAT)Quiescent Current

Feedback Pin Voltage and

Bias Current

TEMPERATURE (°C)

–50

FEEDBACK VOLTAGE (V)

1944-1 G02

1.25

1.24

1.23

1.22

1.21

1.20

BIAS CURRENT (nA)

CURRENT

VOLTAGE

–25 0 25 50 75 100

TEMPERATURE (°C)

QUIESCENT CURRENT (µA)

1944-1 G03

–50 –25 0 25 50 75 100

= 12V

= 1.2V

= 1.23V

NOT SWITCHING

PI FU CTIO S

UUU

FB1 (Pin 1): Feedback Pin for Switcher 1. Set the output

voltage by selecting values for R1 and R2.

SHDN1 (Pin 2): Shutdown Pin for Switcher 1. Tie this pin

to 0.9V or higher to enable device. Tie below 0.25V to turn

it off.

GND (Pin 3): Ground. Tie this pin directly to the local

ground plane.

SHDN2 (Pin 4): Shutdown Pin for Switcher 2. Tie this pin

to 0.9V or higher to enable device. Tie below 0.25V to turn

it off.

FB2 (Pin 5): Feedback Pin for Switcher 2. Set the output

voltage by selecting values for R1B and R2B.

SW2 (Pin 6): Switch Pin for Switcher 2. This is the

collector of the internal NPN power switch. Minimize the

metal trace area connected to the pin to minimize EMI.

PGND (Pins 7, 9): Power Ground. Tie these pins directly

to the local ground plane. Both pins must be tied.

(Pin 8): Input Supply Pin. Bypass this pin with a

capacitor as close to the device as possible.

SW1 (Pin 10): Switch Pin for Switcher 1. This is the

collector of the internal NPN power switch. Minimize the

metal trace area connected to the pin to minimize EMI.

SHUTDOWN PIN VOLTAGE (V)

SHUTDOWN PIN CURRENT (µA)

1944-1 G03

00 5 10 15

25°C

100°C

Switch Off Time Shutdown Pin CurrentSwitch Current Limit

TEMPERATURE (°C)

–50

SWITCH VOLTAGE (V)

0.15

0.13

0.10

0.08

0.05

0.03

0–25 02550

1944-1 G01

75 100

SWITCH

= 100mA

SWITCH

= 70mA

TEMPERATURE (°C)

–50

SWITCH OFF TIME (ns)

–25 025 50 75

2000

1800

1600

1400

1200

1000

800

600

400

200

0100

SWITCHER 2

SWITCHER 1

1944-1 G04

TEMPERATURE (°C)

–50

PEAK CURRENT (mA)

200

175

150

125

100

50 –25 02550

1944-1 G05

75 100

= 12V

= 1.2V

= 12V

= 1.2V SWITCHER 1

SWITCHER 2

LT1944-1

BLOCK DIAGRA

Figure 1. LT1944-1 Block Diagram

OPERATIO

The LT1944-1 uses a constant off-time control scheme to

provide high efficiencies over a wide range of output

current. Operation can be best understood by referring to

the block diagram in Figure 1. Q1 and Q2 along with R3 and

R4 form a bandgap reference used to regulate the output

voltage. When the voltage at the FB1 pin is slightly above

1.23V, comparator A1 disables most of the internal cir-

cuitry. Output current is then provided by capacitor C2,

which slowly discharges until the voltage at the FB1 pin

drops below the lower hysteresis point of A1 (typical

hysteresis at the FB pin is 8mV). A1 then enables the

internal circuitry, turns on power switch Q3, and the

current in inductor L1 begins ramping up. Once the switch

current reaches 100mA, comparator A2 resets the one-

shot, which turns off Q3 for 400ns. L1 then delivers

current to the output through diode D1 as the inductor

current ramps down. Q3 turns on again and the inductor

current ramps back up to 100mA, then A2 resets the one-

shot, again allowing L1 to deliver current to the output.

This switching action continues until the output voltage is

charged up (until the FB1 pin reaches 1.23V), then A1

turns off the internal circuitry and the cycle repeats. The

LT1944-1 contains additional circuitry to provide protec-

tion during start-up and under short-circuit conditions.

When the FB1 pin voltage is less than approximately

600mV, the switch off-time is increased to 1.5µs and the

current limit is reduced to around 70mA (70% of its

normal value). This reduces the average inductor current

and helps minimize the power dissipation in the power

switch and in the external inductor and diode.

The second switching regulator operates in the same

manner, but with a 175mA current limit and an off-time of

1.5µs. With this longer off-time, switcher 2 is ideal for very

low duty cycle applications (i.e. Li-Ion to 5V boost

converters).

–

400ns

ONE-SHOT DRIVER

RESET

DRIVER

RESET

ENABLE

12mV

0.12Ω

140k

30k

40k

X10

FB1

2SHDN1 10 SW1

PGNDGND

1944-1 BD

OUT1

(EXTERNAL)

OUT1

–

1.5µs

ONE-SHOT

ENABLE

21mV

0.12Ω

A2B

A1B

Q3B

R4B

140k

R3B

30k

R6B

40k R5B

40k

Q2B

X10

Q1B

FB2

SHDN2

SW2

PGND

OUT2

R2B

(EXTERNAL)

R1B

(EXTERNAL)

OUT2

SWITCHER 2SWITCHER 1

LT1944-1

Choosing an Inductor

Several recommended inductors that work well with the

LT1944-1 are listed in Table 1, although there are many

other manufacturers and devices that can be used. Con-

sult each manufacturer for more detailed information and

for their entire selection of related parts. Many different

sizes and shapes are available. Use the equations and

recommendations in the next few sections to find the

correct inductance value for your design.

Table 1. Recommended Inductors

PART VALUE (

H) MAX DCR (

Ω

) VENDOR

LQH3C4R7 4.7 0.26 Murata

LQH3C100 10 0.30 (714) 852-2001

LQH3C220 22 0.92 www.murata.com

CD43-4R7 4.7 0.11 Sumida

CD43-100 10 0.18 (847) 956-0666

CDRH4D18-4R7 4.7 0.16 www.sumida.com

CDRH4D18-100 10 0.20

DO1608-472 4.7 0.09 Coilcraft

DO1608-103 10 0.16 (847) 639-6400

DO1608-223 22 0.37 www.coilcraft.com

Inductor Selection—Boost Regulator

The formula below calculates the appropriate inductor

value to be used for a boost regulator using the LT1944-1

(or at least provides a good starting point). This value

provides a good tradeoff in inductor size and system

performance. Pick a standard inductor close to this value.

A larger value can be used to slightly increase the available

output current, but limit it to around twice the value

calculated below, as too large of an inductance will in-

crease the output voltage ripple without providing much

additional output current. A smaller value can be used

(especially for systems with output voltages greater than

12V) to give a smaller physical size. Inductance can be

calculated as:

LVV V

OUT IN MIN D

LIM OFF

=−+

()

where V

= 0.4V (Schottky diode voltage), I

LIM

= 100mA

(or 175mA) and t

OFF

= 400ns (or 1.5µs); for designs with

varying V

such as battery powered applications, use the

minimum V

value in the above equation. For most

APPLICATIO S I FOR ATIO

WUUU

systems with output voltages below 7V, a 10µH inductor

is the best choice, even though the equation above might

specify a smaller value. This is due to the inductor current

overshoot that occurs when very small inductor values are

used (see Current Limit Overshoot section).

For higher output voltages, the formula above will give

large inductance values. For a 2V to 20V converter (typical

LCD Bias application), a 74µH inductor is called for with

the above equation, but a 22µH inductor could be used

without excessive reduction in maximum output current.

Inductor Selection—SEPIC Regulator

The formula below calculates the approximate inductor

value to be used for a SEPIC regulator using the LT1944-1.

As for the boost inductor selection, a larger or smaller

value can be used.

LVV

OUT D

LIM OFF











Current Limit Overshoot

For the constant off-time control scheme of the LT1944-1,

the power switch is turned off only after the current limit

is reached. There is a 100ns delay between the time when

the current limit is reached and when the switch actually

turns off. During this delay, the inductor current exceeds

the current limit by a small amount. The peak inductor

current can be calculated by:

IIVV

Lns

PEAK LIM IN MAX SAT

=+ −











()

100

Where V

SAT

= 0.25V (switch saturation voltage). The

current overshoot will be most evident for systems with

high input voltages and for systems where smaller induc-

tor values are used. This overshoot can be beneficial as it

helps increase the amount of available output current for

smaller inductor values. This will be the peak current seen

by the inductor (and the diode) during normal operation.

For designs using small inductance values (especially at

input voltages greater than 5V), the current limit over-

shoot can be quite high. Although it is internally current

LT1944-1

APPLICATIO S I FOR ATIO

WUUU

limited to 100mA (or 175mA), the power switch of the

LT1944-1 can handle larger currents without problem, but

the overall efficiency will suffer. Best results will be ob-

tained when I

PEAK

is kept below 400mA for the LT1944-1.

Capacitor Selection

Low ESR (Equivalent Series Resistance) capacitors should

be used at the output to minimize the output ripple voltage.

Multilayer ceramic capacitors are the best choice, as they

have a very low ESR and are available in very small

packages. Their small size makes them a good companion

to the LT1944-1’s MS10 package. Solid tantalum capaci-

tors (like the AVX TPS, Sprague 593D families) or OS-CON

capacitors can be used, but they will occupy more board

area than a ceramic and will have a higher ESR. Always use

a capacitor with a sufficient voltage rating.

Ceramic capacitors also make a good choice for the input

decoupling capacitor, which should be placed as close as

possible to the LT1944-1. A 4.7µF input capacitor is

sufficient for most applications. Table 2 shows a list of

several capacitor manufacturers. Consult the manufactur-

ers for more detailed information and for their entire

selection of related parts.

Table 2. Recommended Capacitors

CAPACITOR TYPE VENDOR

Ceramic Taiyo Yuden

(408) 573-4150

www.t-yuden.com

Ceramic AVX

(803) 448-9411

www.avxcorp.com

Ceramic Murata

(714) 852-2001

www.murata.com

Setting the Output Voltage

Set the output voltage for each switching regulator by

choosing the appropriate values for feedback resistors R1

and R2 (see Figure 1).

RRV

OUT

123 1=−











Diode Selection

For most LT1944-1 applications, the Philips BAT54 or

Central Semiconductor CMDSH-3 surface mount Schottky

diodes are an ideal choice. Schottky diodes, with their low

forward voltage drop and fast switching speed, are the

best match for the LT1944-1. Many different manufactur-

ers make equivalent parts, but make sure that the compo-

nent is rated to handle at least 100mA.

Lowering Output Voltage Ripple

Using low ESR capacitors will help minimize the output

ripple voltage, but proper selection of the inductor and the

output capacitor also plays a big role. The LT1944-1

provides energy to the load in bursts by ramping up the

inductor current, then delivering that current to the load.

If too large of an inductor value or too small of a capacitor

value is used, the output ripple voltage will increase

because the capacitor will be slightly overcharged each

burst cycle. To reduce the output ripple, increase the

output capacitor value or add a 4.7pF feed-forward capaci-

tor in the feedback network of the LT1944-1 (see the

circuits in the Typical Applications section). Adding this

small, inexpensive 4.7pF capacitor will greatly reduce the

output voltage ripple.

LT1944-1

TYPICAL APPLICATIO S

Dual Output (5V, 24V) Boost Converter

PACKAGE DESCRIPTIO

MSOP (MS10) 1100

* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,

PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

0.021 ± 0.006

(0.53 ± 0.015)

0° – 6° TYP

SEATING

PLANE

0.007

(0.18)

0.043

(1.10)

MAX

0.007 – 0.011

(0.17 – 0.27) 0.005 ± 0.002

(0.13 ± 0.05)

0.034

(0.86)

REF

0.0197

(0.50)

BSC

12345

0.193 ± 0.006

(4.90 ± 0.15)

8910 76

0.118 ± 0.004*

(3.00 ± 0.102)

0.118 ± 0.004**

(3.00 ± 0.102)

MS10 Package

10-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1661)

SW1

FB2

LT1944-1

22µHD1

SHDN2 53.6k

1µF

24V

1mA

40mA

2.7V

TO 4.2V

C1, C3: TAIYO YUDEN JMK212BJ475

C2: TAIYO YUDEN TMK316BJ105

D1, D2: CENTRAL SEMI CMDSH-3

L1, L2: MURATA LQH3C220

(408) 573-4150

(631) 435-1110

(814) 237-1431

1944-1 TA02

GND

PGND

810

SW2

4.7pF

4.7µF

FB1

SHDN1

22µHD2

324k

4.7pF

4.7µF

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.

LT1944-1

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900

●

FAX: (408) 434-0507

●

www.linear.com

 LINEAR TE CHNOLOGY CORPO RATION 2001

19441f LT/TP 0801 2K • PRINTED IN USA

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Burst Mode is a trademark of Linear Technology Corporation

Four Output Power Supply (±5V, ±15V)

SW2

FB1

LT1944-1

22µHD1

SHDN1 324k

4.7µF

20mA

15V

2mA

–15V

2mA

–5V

20mA

2.7V

TO 4.2V

1944-1 TA03

GND

PGND

SW1

4.7pF

4.7µF

FB2

SHDN2

22µHD2

178k

1µF

4.7pF

C1, C2, C7: TAIYO YUDEN JMK212BJ475

C3, C4: TAIYO YUDEN EMK212BJ105

C5, C6: TAIYO YUDEN EMK107BJ104

D1, D2, D3, D4, D5, D6: CENTRAL SEMI CMDSH3

L1, L2: MURATA LQH3C220

0.1µF

0.1µFC7

4.7µF

1µF

TYPICAL APPLICATIO