1

LT1271/LT1269

4A High Efficiency

Switching Regulators

DESCRIPTIO

S

FEATURE

s

Wide Input Voltage Range 3.5V to 30V

s

Low Quiescent Current: 7mA

s

Internal 4A Switch

s

Very Few External Parts Required

s

Self Protected Against Overloads

s

Shutdown Mode Draws Only 100

µA Supply Current

s

Flyback Regulated Mode Has Fully Floating Outputs

s

Comes in Standard 5-Pin Package

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Can Be Externally Synchronized (See LT1072 Data Sheet)

S

APPLICATI

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Boost Converter

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High Efficiency Buck Converter

s

PC Power Supply with Multiple Outputs

s

Battery Up-Converter

s

Negative-to-Positive Converter

USER NOTE:

This data sheet is only intended to provide specifications, graphs, and a general functional

description of the LT1271/LT1269. Application circuits are included to show the capability of the

LT1271/LT1269. A complete design manual (AN-19) should be obtained to assist in developing new

designs. This manual contains a comprehensive discussion of both the LT1070 and the external

components used with it, as well as complete formulas for calculating the values of these

components. The manual can also be used for the LT1271/LT1269 by factoring in the higher switch

current rating and higher operating frequency.

The LT

switching regulators. Identical to the popular LT1070,

except for switching frequency (LT1271 = 60kHz, LT1269

= 100kHz) and slightly lower switch current, they can be

operated in all standard switching configurations includ-

ing buck, boost, flyback and inverting. A high current, high

efficiency switch is included on the die along with all

oscillator, control and protection circuitry. Integration of

all functions allows the LT1271/LT1269 to be built in a

standard TO-220 power package. This makes them ex-

tremely easy to use and provides “bust proof” operation

similar to that obtained with 3-pin linear regulators.

The LT1271/LT1269 operate with supply voltages from

3.5V to 30V, and draw only 7mA quiescent current. By

utilizing current mode switching techniques, they pro-

vides excellent AC and DC load and line regulation.

A patented adaptive antisat switch drive allows very wide

ranging load currents with no loss in efficiency. An exter-

nally activated shutdown mode reduces total supply cur-

rent to 100

µA typical for standby operation.

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

Burst Mode is a trademark of Linear Technology Corporation.

INPUT VOLTAGE (V)

0

0

10

20

30

5

10

15

20

1271/69 TA02

25

40

50

30

BOOST

BUCK-BOOST

(INVERTING)

FLYBACK

†

BUCK-BOOST

(INVERTING)

BUCK MODE OUTPUT POWER

TRANSFORMER TURNS RATIO MUST BE

OPTIMUM TO ACHIEVE FULL POWER.

†

Maximum Output Power

FB

GND

LT1271

C1

200

µF

35V

0.02

µF

0.1

µF

680

Ω

0.03

µF 4.7µF

TANT

1N4148

L1

25

µH

TO 50

µH

0.015

Ω

390

µF

16V

5V, 3A

< 0.3V = NORMAL RUN MODE

> 2.5V = SHUTDOWN

OPEN = BURST MODE OPERATION

6.5V TO 25V

127/691 TA01

MODE

LT1432

GND

DIODE

MBR

330pF

EFFICIENCY

+

+

+

High Efficiency 5V Regulator with Burst Mode