Datasheet

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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

22µH

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

22µH

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

Summary of content (8 pages)

PAGE 1
LT1944-1 Dual Micropower Step-Up DC/DC Converter U FEATURES ■ ■ ■ ■ ■ ■ DESCRIPTIO 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 LiIon to 5V converter, or a two-cell to 3.3V converter). With an input voltage range of 1.
PAGE 2
LT1944-1 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
LT1944-1 U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Saturation Voltage (VCESAT) Feedback Pin Voltage and Bias Current 0.15 1.25 ISWITCH = 70mA 0.08 0.05 1.23 30 CURRENT 1.22 20 1.21 0.03 0 –50 –25 0 25 50 TEMPERATURE (°C) 75 10 1.20 –50 100 –25 0 25 50 TEMPERATURE (°C) 1944-1 G01 75 23 21 VIN = 12V 19 VIN = 1.
PAGE 4
LT1944-1 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 1.5µs ONE-SHOT Q3B RESET + 0.12Ω 3 R1B (EXTERNAL) R2B (EXTERNAL) R3B 30k R4B 140k 0.
PAGE 5
LT1944-1 U U W U APPLICATIO S I FOR ATIO 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. 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
LT1944-1 U U W U APPLICATIO S I FOR ATIO 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 obtained when IPEAK 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.
PAGE 7
LT1944-1 U TYPICAL APPLICATIO S Dual Output (5V, 24V) Boost Converter L1 22µH VIN 2.7V TO 4.2V D1 24V 1mA 8 10 VIN 2 4.7pF SW1 SHDN1 C1 4.7µF FB1 1M 1 C2 1µF LT1944-1 4 SHDN2 FB2 5 53.6k GND PGND PGND SW2 3 7 9 6 324k 4.7pF L2 22µH 1M C3 4.
PAGE 8
LT1944-1 U TYPICAL APPLICATIO Four Output Power Supply (±5V, ±15V) D5 C6 0.1µF L1 22µH VIN 2.7V TO 4.2V 4 D6 –5V 20mA D1 5V 20mA 8 6 VIN SW2 SHDN2 C1 4.7µF C7 4.7µF FB2 4.7pF 1M 5 C2 4.7µF LT1944-1 2 FB1 SHDN1 1 324k GND PGND PGND SW1 7 3 9 10 178k 4.7pF L2 22µH 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 C3 1µF 2M D2 15V 2mA D3 C5 0.