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LT1305

Micropower High Power

DC/DC Converter with

Low-Battery Detector

■

2-Cell and 3-Cell to 5V Conversion

■

EL Panel Drivers

■

Portable Instruments

ITY

LBI

SHDN

100k

301k

2 TO 3

CELLS

316k

412k

C1

220µF

C2

220µF

SHUTDOWN

LT1305

GND PGND

LBO

LT1305 • TA03

L1

10µH

100k

C1, C2: AVX TPSE227010R0100

D1: MOTOROLA MBRS130LT3

L1: COILCRAFT D03316-103

OUT



5V

400mA

LOW BATTERY

GOES LOW AT

BAT

= 2.2V

LOAD CURRENT (mA)

EFFICIENCY (%)

10 100 1000

LT1305 • TA02

= 4.00V

= 3.00V

= 2.00V

= 2.50V

Efficiency

ESCRIPTIO

■

5V at 400mA from 2V Input

■

Supply Voltage As Low As 1.8V

■

120µA Quiescent Current

■

Low-Battery Detector

■

Low V

CESAT

Switch: 310mV at 2A Typ

■

Uses Inexpensive Surface Mount Inductors

■

8-Lead SO Package

The LT

1305 is a micropower step-up DC/DC converter

that uses Burst Mode

operation. Similar to the LT1303,

the LT1305 features a 2A internal low-loss switch and can

deliver up to four times the output power of the LT1303.

Quiescent current is only 120µA and the Shutdown pin

further reduces current to 10µA. A low-battery detector

provides an open-collector output that goes low when the

input voltage drops below a preset level. The LT1305 is

available in an 8-pin SO, easing board space requirements.

2-Cell and 3-Cell to 5V/400mA DC/DC Converter

with Low-Battery Detect

Burst Mode is a trademark of Linear Technology Corporation

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

Summary of content (8 pages)

PAGE 1
LT1305 Micropower High Power DC/DC Converter with Low-Battery Detector U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ The LT ®1305 is a micropower step-up DC/DC converter that uses Burst ModeTM operation. Similar to the LT1303, the LT1305 features a 2A internal low-loss switch and can deliver up to four times the output power of the LT1303. 5V at 400mA from 2V Input Supply Voltage As Low As 1.
PAGE 2
LT1305 U W W W VIN Voltage .............................................................. 10V SW1 Voltage ............................................................ 25V FB Voltage ............................................................... 10V Shutdown Voltage ................................................... 10V LBO Voltage ............................................................. 10V LBI Voltage .............................................................. 10V Maximum Power Dissipation ...
PAGE 3
LT1305 U W TYPICAL PERFORMANCE CHARACTERISTICS Switch On Time Maximum Duty Cycle Oscillator Frequency 8 200 100 190 95 6 5 4 3 2 –50 – 25 0 25 50 TEMPERATURE (°C) 75 100 180 90 170 85 DUTY CYCLE (%) FREQUENCY (kHz) ON TIME (µs) 7 160 150 140 65 120 60 110 55 100 –50 50 –50 –25 25 50 0 TEMPERATURE (°C) 75 150 140 130 120 100 2.2 400 PEAK SWITCH CURRENT (A) 160 75 2.
PAGE 4
LT1305 U W TYPICAL PERFORMANCE CHARACTERISTICS Low-Battery Detect Trip Point Switch Saturation Voltage 1.235 1.230 1.225 1.220 1.215 1.210 1.205 350 300 250 200 150 100 50 0 –25 25 50 0 TEMPERATURE (°C) 75 100 SWITCH SATURATION VOLTAGE (mV) SWITCH SATURATION VOLTAGE (mV) 1.240 LBI VOLTAGE (V) 300 TA = 25°C 1.245 1.200 –50 Switch Saturation Voltage 400 1.250 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.
PAGE 5
LT1305 W BLOCK DIAGRAM D1 L1 VIN + C5 6 VIN 7 + HYSTERETIC COMPARATOR OFF – OSCILLATOR C1 R2 REFERENCE 1.24V – FB C4 R1 3Ω C2 4 + 36mV CURRENT COMPARATOR R1 SW A3 DRIVER Q2 1× Q1 160× + – C3 + GND 1 LBI 5 LBO 2 SHUTDOWN 3 8 PGND LT1305 • F01 Figure 1. LT1305 Block Diagram U OPERATION Operation of the LT1305 is best understood by referring to the Block Diagram in Figure 1.
PAGE 6
LT1305 U OPERATION If switch current reaches 2A, causing C2 to trip, switch on time is reduced and off time increases slightly. This allows continuous operation during bursts. C2 monitors the voltage across 3Ω resistor R1 which is directly related to the switch current. Q2’s collector current is set by the emitter-area ratio to 0.6% of Q1’s collector current.
PAGE 7
LT1305 U TYPICAL APPLICATIONS N Setting Output Voltage 4-Cell-to-5V Converter 1N5817 L1 VIN VIN + SW R2 GND MBRS130LT3 SW 5V 400mA 100µF LT1305 + 309k 4 CELLS SHDN 220µF FB PGND +100µF** VIN + VOUT LT1305 100µF L1* 22µH 3.5V to 6.5V FB PGND GND R1 22µH* + 150µF** 100k SHUTDOWN ( ) VOUT = 1.24V 1 + R2 R1 * COILCRAFT DO3316-223 OR SUMIDA CD105-220 ** SANYO OS-CON LT1305 • TA03 LT1305 • TA05 5V Step-Up Converter with Reference Output 100k VIN 2N3906 VREF OUTPUT 1.
PAGE 8
LT1305 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic SOIC 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157* (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 2 3 4 0.053 – 0.069 (1.346 – 1.752) 0.004 – 0.010 (0.101 – 0.254) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 0.050 (1.