LT1270A/LT1270
8A and 10A High Efficiency
Switching Regulators
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FEATURES
DESCRIPTIO
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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
extremelyeasytouseandprovides“bustproof”operation
similar to that obtained with 3-pin linear regulators.
Wide Input Voltage Range: 3.5V to 30V
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Low Quiescent Current: 7mA
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Internal 8A Switch (10A for LT1270A)
Very Few External Parts Required
Self-Protected Against Overloads
Shutdown Mode Draws Only 100µA Supply Current
Flyback-Regulated Mode Has Fully Floating Outputs
Can be Externally Synchronized
(See LT1072 Data Sheet)
Comes in Standard 5-Pin TO-220 Package
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APPLICATIO S
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.
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High Efficiency Buck Converter
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PC Power Supply with Multiple Outputs
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Battery Upconverter
Negative-to-Positive Converter
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TheLT1270A/LT1270useadaptiveanti-satswitchdriveto
allow very wide ranging load currents with no loss in
efficiency. An externally activated shutdown mode re-
duces total supply current to 100µA typical for standby
operation.
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.
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TYPICAL APPLICATIO
Maximum Output Power*
High Efficiency† Buck Converter
100
BOOST
†EFFICIENCY IS ≈ 88% @ 2A, 86% @ 5A.
V
IN
(8V TO 25V)
FOR µPOWER SHUTDOWN OPTION, CONSULT FACTORY.
BUCK-BOOST,
= 12V
V
V
80
60
SW
V
*THESE COMPONENTS RATED CONSERVATIVELY TO
IMPROVE EFFICIENCY. MAXIMUM OUTPUT CURRENT
CAN BE 7A. FOR HIGH EFFICIENCY, THE INDUCTOR SHOULD
BE MOLYPERMALLOY OR FERRITE.
O
1N5819
LT1270*
(INVERTING)
FB
IN
FLYBACK†
GND
V
C
+
1µF
0.047µF
0.047µF
40
1k
35µH, 8A*
5V*
5A
BUCK-BOOST, V = 5V
O
20
0
(INVERTING)
9.1k
10k
ANODE
+
LT1431CZ REF
CATHODE
470µF
35V
MBR1035*
2N3904
0
5
15
20
25
30
10
INPUT VOLTAGE (V)
LT1270 • TA02
1N4158
560Ω
1000µF
*MULTIPLY BY 1.2 FOR LT1270A.
360Ω
25V
BUCK MODE OUTPUT POWER ≈ (7.5A)(V
)
OUT
† TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER
LT1270 • TA01
1270afc
1