LT1269_15 Datasheet, PDF (1/8 Pages) Linear Technology – 4A High Efficiency Switching Regulators

LT1271/LT1269
4A High Efficiency
Switching Regulators
FEATURES
DESCRIPTIO
s _{Wide Input Voltage Range 3.5V to 30V}
The LT^®1271 and LT1269 are monolithic high power
s _{Low Quiescent Current: 7mA}
switching regulators. Identical to the popular LT1070,
s _{Internal 4A Switch}
except for switching frequency (LT1271 = 60kHz, LT1269
s _{Very Few External Parts Required}
= 100kHz) and slightly lower switch current, they can be
s _{Self Protected Against Overloads}
operated in all standard switching configurations includ-
s _{Shutdown Mode Draws Only 100µA Supply Current}
s _{Flyback Regulated Mode Has Fully Floating Outputs}
ing buck, boost, flyback and inverting. A high current, high
efficiency switch is included on the die along with all
s _{Comes in Standard 5-Pin Package}
oscillator, control and protection circuitry. Integration of
s _{Can Be Externally Synchronized (See LT1072 Data Sheet) all functions allows the LT1271/LT1269 to be built in a}
APPLICATI S
standard TO-220 power package. This makes them ex-
tremely easy to use and provides “bust proof” operation
s _{Boost Converter}
similar to that obtained with 3-pin linear regulators.
s _{High Efficiency Buck Converter}
s _{PC Power Supply with Multiple Outputs}
s _{Battery Up-Converter}
s _{Negative-to-Positive Converter}
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 pro-
vides 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 exter-
nally activated shutdown mode reduces total supply cur-
rent 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.
TYPICAL APPLICATION
High Efficiency 5V Regulator with Burst Mode^TM Operation
V_IN
6.5V TO 25V
C1 +
200µF
35V
V_SW
V_IN
LT1271
FB
V_C
GND
0.02µF
680Ω
0.1µF
+
0.03µF 4.7µF
TANT
MBR
330pF
EFFICIENCY ≈ 90%
AT I_OUT = 0.4A TO 1.5A
1N4148
L1
25µH
TO 50µH
0.015Ω
V_OUT
5V, 3A
+ _390µF
16V
V_C DIODE
V_IN
LT1432
MODE
GND
V⁺
V_LIM
V_OUT
< 0.3V = NORMAL RUN MODE
> 2.5V = SHUTDOWN
OPEN = BURST MODE OPERATION
127/691 TA01
Maximum Output Power
50
BOOST
BUCK-BOOST
40
V_O = 12V
(INVERTING)
30
FLYBACK^†
20
10
BUCK-BOOST
V_O = 5V
(INVERTING)
0
0
5 10 15 20 25 30
INPUT VOLTAGE (V)
1271/69 TA02
BUCK MODE OUTPUT POWER ≈ (3.5A)(V_OUT)
†_{TRANSFORMER TURNS RATIO MUST BE}
OPTIMUM TO ACHIEVE FULL POWER.
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