LT1270A Datasheet, PDF (1/4 Pages) Linear Technology – 8A and 10A High Efficiency Switching Regulators

LT1270A/LT1270
8A and 10A High Efficiency
Switching Regulators
FEATURES
s _{Wide Input Voltage Range: 3.5V to 30V}
s _{Low Quiescent Current: 7mA}
s _{Internal 8A Switch (10A for LT1270A)}
s _{Very Few External Parts Required}
s _{Self-Protected Against Overloads}
s _{Shutdown Mode Draws Only 100µA Supply Current}
s _{Flyback-Regulated Mode Has Fully Floating Outputs}
s _{Comes in Standard 5-Pin Package}
s _{Can be Externally Synchronized}
(See LT1072 Data Sheet)
APPLICATI S
s _{High Efficiency Buck Converter}
s _{PC Power Supply with Multiple Outputs}
s _{Battery Upconverter}
s _{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.
DESCRIPTIO
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 100µA typical for standby
operation.
TYPICAL APPLICATI
High Efficiency^† Buck Converter
V_IN
(8V TO 25V)
V_SW
1N5819
LT1270*
V_IN
FB
GND V_C
†_{EFFICIENCY IS ≈ 88% @ 2A, 86% @ 5A.}
FOR µPOWER 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.
1µF
470µF
35V
0.047µF
1k
0.047µF
35µH, 8A*
MBR1035*
2N3904
360Ω
ANODE
LT1431CZ REF
CATHODE
1N4158
560Ω
5V*
5A
9.1k
10k
1000µF
25V
LT1270 • TA01
Maximum Output Power*
100
BOOST
80
BUCK-BOOST,
V_O = 12V
(INVERTING)
60
FLYBACK^†
40
20
BUCK-BOOST, V_O = 5V
(INVERTING)
0
0
5 10 15 20 25 30
INPUT VOLTAGE (V)
LT1270 • TA02
*MULTIPLY BY 1.2 FOR LT1270A.
BUCK MODE OUTPUT POWER ≈ (7.5A)(V_OUT)
† _{TRANSFORMER TURNS RATIO MUST BE}
OPTIMUM TO ACHIEVE FULL POWER
1