LT1271/LT1269
4A High Efficiency
Switching Regulators
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
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 100碌A Supply Current
Flyback Regulated Mode Has Fully Floating Outputs
Comes in Standard 5-Pin Package
Can Be Externally Synchronized (See LT1072 Data Sheet)
APPLICATI
s
s
s
s
s
S
Boost Converter
High Efficiency Buck Converter
PC Power Supply with Multiple Outputs
Battery Up-Converter
Negative-to-Positive Converter
The LT
廬
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 includ-
ing 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 ex-
tremely easy to use and provides 鈥渂ust proof鈥?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 pro-
vides excellent AC and DC load and line regulation.
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 100碌A typical for standby operation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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.
TYPICAL APPLICATION
High Efficiency 5V Regulator with Burst Mode
TM
Operation
50
V
IN
6.5V TO 25V
V
SW
LT1271
FB
V
C
0.02碌F
680鈩?/div>
0.1碌F
0.03碌F 4.7碌F
TANT
GND
1N4148
V
IN
OUTPUT POWER (W)
EFFICIENCY
鈮?/div>
90%
AT I
OUT
= 0.4A TO 1.5A
+
L1
25碌H
TO 50碌H
0.015鈩?/div>
MBR
330pF
V
+
V
LIM
LT1432
V
OUT
MODE
GND
+
V
OUT
5V, 3A
390碌F
16V
V
C
C1
200碌F
35V
DIODE
+
V
IN
< 0.3V = NORMAL RUN MODE
> 2.5V = SHUTDOWN
OPEN = BURST MODE OPERATION
127/691 TA01
U
Maximum Output Power
40
BOOST
BUCK-BOOST
V
O
= 12V
(INVERTING)
30
FLYBACK
鈥?/div>
20
BUCK-BOOST
V
O
= 5V
(INVERTING)
0
5
15
20
10
INPUT VOLTAGE (V)
25
30
10
0
1271/69 TA02
U
UO
BUCK MODE OUTPUT POWER
鈮?/div>
(3.5A)(V
OUT
)
鈥?/div>
TRANSFORMER TURNS RATIO MUST BE
OPTIMUM TO ACHIEVE FULL POWER.
1
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