FEATURE
A
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.
TYPICAL
(8V TO 25V)
PPLICATI
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
Comes in Standard 5-Pin Package
Can be Externally Synchronized
(See LT1072 Data Sheet)
High Efficiency Buck Converter
PC Power Supply with Multiple Outputs
Battery Upconverter
Negative-to-Positive Converter
V
IN
+
470 F
35V
S
A
+
1N5819
1 F
O
PPLICATI
U
V
V
SW
IN
S
GND
LT1270*
High Efficiency
MBR1035*
V
C
1k
FB
0.047 F
O
2N3904
U
360
†
Buck Converter
35 H, 8A*
IMPROVE EFFICIENCY. MAXIMUM OUTPUT CURRENT
0.047 F
†
FOR
*THESE COMPONENTS RATED CONSERVATIVELY TO
CAN BE 7A. FOR HIGH EFFICIENCY, THE INDUCTOR SHOULD
BE MOLYPERMALLOY OR FERRITE.
EFFICIENCY IS 88% @ 2A, 86% @ 5A.
POWER SHUTDOWN OPTION, CONSULT FACTORY.
LT1431CZ
CATHODE
ANODE
560
1N4158
REF
9.1k
10k
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.
D
ESCRIPTIO
1000 F
25V
5V*
5A
8A and 10A High Efficiency
LT1270 • TA01
Switching Regulators
U
100
80
60
40
20
0
0
*MULTIPLY BY 1.2 FOR LT1270A.
†
BUCK MODE OUTPUT POWER (7.5A)(V
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
O
25
LT1270 • TA02
= 5V
OUT
)
30
1