LT1271/LT1269
4A High Efficiency
Switching Regulators
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DESCRIPTIO
FEATURES
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Wide Input Voltage Range 3.5V to 30V
Low Quiescent Current: 7mA
Internal 4A Switch
Very Few External Parts Required
Self Protected Against Overloads
Shutdown Mode Draws Only 100µA Supply Current
Flyback Regulated Mode Has Fully Floating Outputs
Comes in Standard 5-Pin Package
Can Be Externally Synchronized (See LT1072 Data Sheet)
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APPLICATI
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Boost Converter
High Efficiency Buck Converter
PC Power Supply with Multiple Outputs
Battery Up-Converter
Negative-to-Positive Converter
The LT®1271 and LT1269 are monolithic high power
switching regulators. Identical to the popular LT1070,
except for switching frequency (LT1271 = 60kHz, LT1269
= 100kHz) and slightly lower switch current, they can be
operated in all standard switching configurations 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. Integration of
all functions allows the LT1271/LT1269 to be built in a
standard TO-220 power package. This makes them extremely easy to use and provides “bust proof” operation
similar to that obtained with 3-pin linear regulators.
The LT1271/LT1269 operate with supply voltages from
3.5V to 30V, and draw only 7mA quiescent current. By
utilizing current mode switching techniques, they provides excellent AC and DC load and line regulation.
USER NOTE:
This data sheet is only intended to provide specifications, graphs, and a general functional
description of the LT1271/LT1269. Application circuits are included to show the capability of the
LT1271/LT1269. A complete design manual (AN-19) should be obtained to assist in developing new
designs. This manual 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. The manual can also be used for the LT1271/LT1269 by factoring in the higher switch
current rating and higher operating frequency.
A patented adaptive antisat switch drive allows very wide
ranging load currents with no loss in efficiency. An externally activated shutdown mode reduces total supply current to 100µA typical for standby operation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATION
High Efficiency 5V Regulator with Burst ModeTM Operation
Maximum Output Power
50
VSW
VIN
FB
VC
GND
1N4148
0.02µF
680Ω
0.03µF 4.7µF
TANT
0.1µF
+
L1
25µH
TO 50µH
MBR
330pF
VC
C1
200µF
35V
+
DIODE
0.015Ω
+
VOUT
5V, 3A
390µF
16V
30
BUCK-BOOST
VO = 12V
(INVERTING)
FLYBACK†
20
BUCK-BOOST
VO = 5V
(INVERTING)
10
0
0
V+
5
15
20
10
INPUT VOLTAGE (V)
25
30
1271/69 TA02
VLIM
VIN
LT1432
†
VOUT
MODE
BOOST
40
EFFICIENCY ≈ 90%
AT IOUT = 0.4A TO 1.5A
LT1271
OUTPUT POWER (W)
VIN
6.5V TO 25V
BUCK MODE OUTPUT POWER ≈ (3.5A)(VOUT)
TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER.
GND
< 0.3V = NORMAL RUN MODE
> 2.5V = SHUTDOWN
OPEN = BURST MODE OPERATION
127/691 TA01
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