FEATURES
TYPICAL APPLICATIO
APPLICATIO S
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.
(8V TO 25V)
Wide Input Voltage Range: 3.5V to 30V
Low Quiescent Current: 7mA
Internal 8A Switch (10A for LT1270A)
Very Few External Parts Required
Self-Protected Against Overloads
Shutdown Mode Draws Only 100 A 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
High Efficiency Buck Converter
PC Power Supply with Multiple Outputs
Battery Upconverter
Negative-to-Positive Converter
V
IN
+
470 F
35V
+
1N5819
1 F
U
V
V
SW
IN
GND
LT1270*
High Efficiency
MBR1035*
V
C
1k
FB
0.047 F
2N3904
U
360
†
Buck Converter
35 H, 8A*
0.047 F
†
*THESE COMPONENTS RATED CONSERVATIVELY TO
EFFICIENCY IS
FOR POWER SHUTDOWN OPTION, CONSULT FACTORY.
IMPROVE EFFICIENCY. MAXIMUM OUTPUT CURRENT
CAN BE 7A. FOR HIGH EFFICIENCY, THE INDUCTOR SHOULD
BE MOLYPERMALLOY OR FERRITE.
LT1431CZ
CATHODE
ANODE
560
1N4158
88% @ 2A, 86% @ 5A.
REF
9.1k
10k
DESCRIPTIO
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 A typical for standby
operation.
1000 F
25V
5V*
5A
LT1270 • TA01
8A and 10A High Efficiency
Switching Regulators
U
100
80
60
40
20
0
0
*MULTIPLY BY 1.2 FOR LT1270A.
†
BUCK MODE OUTPUT POWER
OPTIMUM TO ACHIEVE FULL POWER
TRANSFORMER TURNS RATIO MUST BE
LT1270A/LT1270
Maximum Output Power*
5
INPUT VOLTAGE (V)
BOOST
10
FLYBACK
BUCK-BOOST,
BUCK-BOOST, V
(INVERTING)
(INVERTING)
15
†
V
O
= 12V
20
(7.5A)(V
O
25
LT1270 • TA02
= 5V
OUT
1270afc
)
30
1