LT1506
4.5A, 500kHz Step-Down
Switching Regulator
FEATURES
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DESCRIPTION
The LT
®
1506 is a 500kHz monolithic buck mode switching
regulator functionally identical to the LT1374 but optimized
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
switching frequency allows a considerable reduction in the
size of external components. The topology is current mode
for fast transient response and good loop stability. Both
fixed output voltage and adjustable parts are available.
A special high speed bipolar process and new design tech-
niques achieve high efficiency at high switching frequency.
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.
The LT1506 fits into standard 7-pin DD and fused lead
SO-8 packages. Full cycle-by-cycle short-circuit protection
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. A shutdown signal reduces supply current
to 20µA. Synchronization allows an external logic level sig-
nal to increase the internal oscillator from 580kHz to 1MHz.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Constant 500kHz Switching Frequency
Easily Synchronizable
Operates with Input as Low as 4V
Uses All Surface Mount Components
Inductor Size Reduced to 1.8
µ
H
Saturating Switch Design: 0.07Ω
Shutdown Current: 20µA
Cycle-by-Cycle Current Limiting
APPLICATIONS
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Portable Computers
Battery-Powered Systems
Battery Charger
Distributed Power
TYPICAL APPLICATION
5V to 3.3V Down Converter
D2
1N914
C2
0.68µF
INPUT
5V
BOOST
V
IN
V
SW
LT1506-3.3
SHDN
GND
SENSE
V
C
C
C
1.5nF
D1
MBRS330T3
L1
5µH
OUTPUT
3.3V
4A
EFFICIENCY (%)
90
V
OUT
= 3.3V
V
IN
= 5V
L = 10µH
85
80
C3
10µF TO
50µF
CERAMIC
+
OPEN
OR
HIGH
= ON
75
+
C1
100µF, 10V
SOLID
TANTALUM
1506 TA01
70
0
0.5
1.0
1.5 2.0 2.5 3.0
LOAD CURRENT (A)
3.5
4.0
U
U
U
Efficiency vs Load Current
1506 TA02
1
LINER [ LINEAR TECHNOLOGY ]
