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LT1944

Dual Micropower Step-Up

DC/DC Converter

The LT

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

verter in a 10-pin MSOP package. Each converter is

designed with a 350mA current limit and an input voltage

range of 1.2V to 15V, making the LT1944 ideal for a wide

variety of applications. Both converters feature a quies-

cent 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, resulting in

high efficiency over a broad range of load current. The 36V

switch allows high voltage outputs up to 34V to be easily

generated in a simple boost topology without the use of

costly transformers. The LT1944’s low off-time of 400ns

permits the use of tiny, low profile inductors and capaci-

tors 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

Switch: 250mV at 300mA

■

Uses Small Surface Mount Components

■

High Output Voltage: Up to 34V

■

Tiny 10-Pin MSOP Package

■

LCD Bias

■

Handheld Computers

■

Battery Backup

■

Digital Cameras

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

SW1

FB2

LT1944

4.7µH

SHDN2

324k

10µF

80mA

30V

8mA

2.7V

TO 4.2V

1944 TA01

GND

PGND

810

SW2

4.7pF

4.7µF

FB1

SHDN1

10µH

86.6k

1µF

4.7pF

C1: TAIYO YUDEN JMK212BJ475

C2: TAIYO YUDEN JMK316BJ106

C3: TAIYO YUDEN GMK316BJ105

D1, D2: ON SEMI MBR0540

L1: MURATA LQH3C4R7

L2: MURATA LQH3C100

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

1 10 100

1944 TA01a

= 4.2V

= 2.7V

Dual Output (5V, 30V) Boost Converter 5V Output Efficiency

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (8 pages)

PAGE 1
LT1944 Dual Micropower Step-Up DC/DC Converter U FEATURES ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT®1944 is a dual micropower step-up DC/DC converter in a 10-pin MSOP package. Each converter is designed with a 350mA current limit and an input voltage range of 1.2V to 15V, making the LT1944 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.
PAGE 2
LT1944 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) VIN, SHDN1, SHDN2 Voltage ................................... 15V SW1, SW2 Voltage .................................................. 36V FB1, FB2 Voltage .......................................................VIN Current into FB1, FB2 Pins ..................................... 1mA Junction Temperature ........................................... 125°C Operating Temperature Range (Note 2) ..
PAGE 3
LT1944 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Saturation Voltage (VCESAT) Feedback Pin Voltage and Bias Current 0.60 Quiescent Current 1.25 25 50 VFB = 1.23V NOT SWITCHING FEEDBACK VOLTAGE (V) 1.24 0.45 ISWITCH = 500mA 0.40 0.35 0.30 ISWITCH = 300mA 0.25 0.20 40 VOLTAGE 1.23 30 CURRENT 1.22 20 1.21 10 BIAS CURRENT (nA) SWITCH VOLTAGE (V) 0.50 QUIESCENT CURRENT (µA) 0.55 23 21 VIN = 12V 19 VIN = 1.2V 17 0.15 0.10 –50 –25 0 25 50 TEMPERATURE (°C) 75 1.
PAGE 4
LT1944 W BLOCK DIAGRA D2 D1 L1 VOUT1 VIN 8 VIN 2 SHDN1 10 VIN C3 C2 C1 L2 VOUT2 SW1 SW2 SHDN2 6 4 VIN R5 40k R6 40k R6B 40k + A1 A1B ENABLE ENABLE R5B 40k + VOUT1 VOUT2 – R1 (EXTERNAL) FB1 – Q1B 1 Q1 Q2 X10 R2 (EXTERNAL) 400ns ONE-SHOT Q3 DRIVER R3 30k 400ns ONE-SHOT Q3B RESET + GND 3 FB2 R1B (EXTERNAL) R2B (EXTERNAL) R3B 30k + R4 140k 0.12Ω – 5 DRIVER RESET A2 Q2B X10 R4B 140k 0.12Ω 42mV 42mV 9 PGND PGND – A2B 7 1944 BD Figure 1.
PAGE 5
LT1944 U U W U APPLICATIO S I FOR ATIO Choosing an Inductor Several recommended inductors that work well with the LT1944 are listed in Table 1, although there are many other manufacturers and devices that can be used. Consult 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.
PAGE 6
LT1944 U U W U APPLICATIO S I FOR ATIO limited to 350mA, the power switch of the LT1944 can handle larger currents without problem, but the overall efficiency will suffer. Best results will be obtained when IPEAK is kept below 700mA for the LT1944. Capacitor Selection Low ESR (Equivalent Series Resistance) capacitors should be used at the output to minimize the output ripple voltage.
PAGE 7
LT1944 U TYPICAL APPLICATIO S 2-Cell Dual Output (3.3V, 5V) Boost Converter L1 4.7µH VIN 1.8V TO 3V D1 5V 40mA 8 10 VIN 2 4.7pF SW1 SHDN1 C1 4.7µF FB1 1M 1 C2 10µF LT1944 4 SHDN2 FB2 5 324k GND PGND PGND SW2 7 3 9 6 604k C1: TAIYO YUDEN JMK212BJ475 C2, C3: TAIYO YUDEN JMK316BJ106 D1, D2: ON SEMI MBR0520 L1, L2: MURATA LQH3C4R7 (408) 573-4150 (408) 573-4150 (800) 282-9855 (814) 237-1431 4.7pF L2 4.7µH 1M C3 10µF D2 3.3V 80mA 1944 TA02 2-Cell to 5V Efficiency 2-Cell to 3.
PAGE 8
LT1944 U TYPICAL APPLICATIO Four Output Power Supply for Color LCD Displays Q1 D3A C6 2.2µF C7 0.1µF –6.5V 500µA Q2 140k D3B D2B C3 0.1µF C4 0.1µF L1 10µH VIN 2.7V TO 4.2V D2A D1 10V 5mA 8 10 VIN 2 20V C5 500µA 1µF 1M SW1 SHDN1 C1 4.7µF 1 FB1 C2 2.2µF LT1944 4 SHDN2 5 FB2 140k GND PGND PGND SW2 3 7 9 6 C8 1µF L2 10µH 82.