LT1506
4.5A, 500kHz Step-Down
Switching Regulator
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DESCRIPTION
FEATURES
TheLT®1506isa500kHzmonolithicbuckmodeswitching
regulatorfunctionallyidenticaltotheLT1374butoptimized
for lower input voltage applications. It will operate over a
4V to 15V input range compared with 5.5V to 25V for the
LT1374. A 4.5A switch is included on the die along with all
the necessary oscillator, control and logic circuitry. High
switchingfrequencyallowsaconsiderablereductioninthe
sizeofexternalcomponents.Thetopologyiscurrentmode
for fast transient response and good loop stability. Both
fixed output voltage and adjustable parts are available.
■
Constant 500kHz Switching Frequency
■
Easily Synchronizable
■
Operates with Input as Low as 4V
■
Uses All Surface Mount Components
■
Inductor Size Reduced to 1.8µH
■
■
■
Saturating Switch Design: 0.07Ω
Shutdown Current: 20µA
Cycle-by-Cycle Current Limiting
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APPLICATIONS
Aspecialhighspeedbipolarprocessandnewdesigntech-
niquesachievehighefficiencyathighswitchingfrequency.
Efficiency is maintained over a wide output current range
by keeping quiescent supply current to 4mA and by utiliz-
ing a supply boost capacitor to saturate the power switch.
■
Portable Computers
■
Battery-Powered Systems
■
Battery Charger
Distributed Power
■
The LT1506 fits into standard 7-pin DD and fused lead
SO-8packages.Fullcycle-by-cycleshort-circuitprotection
and thermal shutdown are provided. Standard surface
mount external parts are used, including the inductor and
capacitors. There is the optional function of shutdown or
synchronization.Ashutdownsignalreducessupplycurrent
to20µA.Synchronizationallowsanexternallogiclevelsig-
naltoincreasetheinternaloscillatorfrom580kHzto1MHz.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
Efficiency vs Load Current
90
V
V
= 3.3V
5V to 3.3V Down Converter
OUT
IN
= 5V
L = 10µH
D2
1N914
85
80
75
70
C2
0.68µF
L1
5µH
OUTPUT
3.3V
BOOST
INPUT
5V
V
V
SW
IN
4A
C3
OPEN
OR
HIGH
= ON
LT1506-3.3
+
10µF TO
50µF
CERAMIC
SHDN
GND
SENSE
C
V
C1
+
100µF, 10V
SOLID
TANTALUM
C
D1
MBRS330T3
C
1.5nF
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
LOAD CURRENT (A)
1506 TA01
1506 TA02
1