Datasheet
1
LT1270A/LT1270
1270afc
DESCRIPTIO
U
TYPICAL APPLICATIO
U
APPLICATIO S
U
FEATURES
8A and 10A High Efficiency
Switching Regulators
■
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 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
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 100µA typical for standby
operation.
■
High Efficiency Buck Converter
■
PC Power Supply with Multiple Outputs
■
Battery Upconverter
■
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.
V
SW
V
IN
FB
V
C
GND
MBR1035*
LT1270*
0.047µF
1k
0.047µF1µF
35µH, 8A*
ANODE
LT1431CZ
CATHODE
REF
1N4158
9.1k
10k
+
470µF
35V
V
IN
(8V TO 25V)
2N3904
360Ω 560Ω
1000µF
25V
5V*
5A
+
†
EFFICIENCY IS ≈ 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
†
Buck Converter
Maximum Output Power*
INPUT VOLTAGE (V)
0
0
OUTPUT POWER (W)
20
40
60
5
10
15 20
LT1270 • TA02
25
80
100
30
BOOST
FLYBACK
†
BUCK-BOOST, V
O
= 5V
(INVERTING)
BUCK-BOOST,
V
O
= 12V
(INVERTING)
*MULTIPLY BY 1.2 FOR LT1270A.
BUCK MODE OUTPUT POWER ≈ (7.5A)(V
OUT
)
†
TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER