LT1270A/LT1270
8A and 10A High Efficiency
Switching Regulators
FEATURES
s
s
s
s
s
s
s
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DESCRIPTIO
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碌A(chǔ) Supply Current
Flyback-Regulated Mode Has Fully Floating Outputs
Comes in Standard 5-Pin Package
Can be Externally Synchronized
(See LT1072 Data Sheet)
APPLICATI
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S
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 鈥渂ust proof鈥?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碌A(chǔ) 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.
TYPICAL APPLICATI
V
IN
(8V TO 25V)
1N5819
V
IN
V
SW
LT1270*
High Efficiency
鈥?/div>
Buck Converter
100
EFFICIENCY IS
鈮?/div>
88% @ 2A, 86% @ 5A.
FOR
碌POWER
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.
鈥?/div>
FB
GND
V
C
0.047碌F
1k
OUTPUT POWER (W)
+
1碌F
0.047碌F
35碌H, 8A*
5V*
5A
ANODE
9.1k
+
470碌F
35V
MBR1035*
2N3904
360鈩?/div>
LT1431CZ REF
CATHODE
10k
1N4158
560鈩?/div>
1000碌F
25V
LT1270 鈥?TA01
U
Maximum Output Power*
BOOST
BUCK-BOOST,
V
O
= 12V
(INVERTING)
FLYBACK
鈥?/div>
80
60
40
20
BUCK-BOOST, V
O
= 5V
(INVERTING)
0
0
5
15
20
10
INPUT VOLTAGE (V)
25
30
LT1270 鈥?TA02
UO
UO
*MULTIPLY BY 1.2 FOR LT1270A.
BUCK MODE OUTPUT POWER
鈮?/div>
(7.5A)(V
OUT
)
鈥?/div>
TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER
1
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