1

LT1270A/LT1270

DESCRIPTIO

S

FEATURE

8A and 10A High Efficiency

Switching Regulators

s

Wide Input Voltage Range: 3.5V to 30V

s

Low Quiescent Current: 7mA

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Internal 8A Switch (10A for LT1270A)

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Very Few External Parts Required

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Self-Protected Against Overloads

s

Shutdown Mode Draws Only 100

µA Supply Current

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Flyback-Regulated Mode Has Fully Floating Outputs

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Comes in Standard 5-Pin Package

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Can be Externally Synchronized

(See LT1072 Data Sheet)

The LT1270A/LT1270 are monolithic high power switch-

ing regulators. Identical to the popular LT1070, except for

switching frequency (60kHz) and higher switch current,

they can be operated in all standard switching configura-

tions including buck, boost, flyback, and inverting. A high

current, high efficiency switch is included on the die along

with all oscillator, control, and protection circuitry. Inte-

gration of all functions allows the LT1270A/LT1270 to be

built in a standard TO-220 power package. This makes it

extremely easy to use and provides “bust proof” operation

similar to that obtained with 3-pin linear regulators.

The LT1270A/LT1270 operate with supply voltages from

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

utilizing current-mode switching techniques, they provide

excellent AC and DC load and line regulation.

The LT1270A/LT1270 use adaptive anti-sat switch drive to

allow very wide ranging load currents with no loss in

efficiency. An externally activated shutdown mode re-

duces total supply current to 100

µA typical for standby

operation.

S

APPLICATI

s

High Efficiency Buck Converter

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PC Power Supply with Multiple Outputs

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Battery Upconverter

s

Negative-to-Positive Converter

USER NOTE:

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

description of the LT1270A/LT1270. Application circuits are included to show the capability of the

LT1270A/LT1270. A complete design manual (AN-19) should be obtained to assist in developing

new designs. AN-19 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. AN-19 can also be used for the LT1270A/LT1270 by factoring in the higher switch

current rating and higher operating frequency.

A comprehensive CAD program called SwitcherCad is also available. Contact the local sales office

in your area or the factory direct.

APPLICATI

TYPICAL

FB

GND

MBR1035*

LT1270*

0.047

µF

1k

0.047

µF

1

µF

35

µH, 8A*

ANODE

LT1431CZ

CATHODE

REF

1N4158

9.1k

10k

+

470

µF

35V

(8V TO 25V)

2N3904

360

Ω

560

Ω

1000

µF

25V

5V*

5A

+

≈ 88% @ 2A, 86% @ 5A.

FOR

µPOWER SHUTDOWN OPTION, CONSULT FACTORY.

*THESE COMPONENTS RATED CONSERVATIVELY TO

IMPROVE EFFICIENCY. MAXIMUM OUTPUT CURRENT

CAN BE 7A. FOR HIGH EFFICIENCY, THE INDUCTOR SHOULD

BE MOLYPERMALLOY OR FERRITE.

LT1270 • TA01

1N5819

High Efficiency

Maximum Output Power*

INPUT VOLTAGE (V)

0

0

20

40

60

5

10

15

20

LT1270 • TA02

25

80

100

30

BOOST

FLYBACK

†

(INVERTING)

BUCK-BOOST,

(INVERTING)

*MULTIPLY BY 1.2 FOR LT1270A.

BUCK MODE OUTPUT POWER

OPTIMUM TO ACHIEVE FULL POWER