LT1576/LT1576-5
1.5A, 200kHz Step-Down
Switching Regulator
FEATURES
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DESCRIPTIO
Constant 200kHz Switching Frequency
1.21V Reference Voltage
Fixed 5V Output Option
Easily Synchronizable
Uses All Surface Mount Components
Inductor Size Reduced to 15
µ
H
Saturating Switch Design: 0.2Ω
Effective Supply Current: 1.16mA
Shutdown Current: 20µA
Cycle-by-Cycle Current Limiting
Fused Lead SO-8 Package
The LT
®
1576 is a 200kHz monolithic buck mode switching
regulator. A 1.5A switch is included on the die along with
all the necessary oscillator, control and logic circuitry. The
topology is current mode for fast transient response and
good loop stability. The LT1576 is a modified version of the
industry standard LT1376 optimized for noise sensitive
applications.
In addition, the reference voltage has been lowered to
allow the device to produce output voltages down to 1.2V.
Quiescent current has been reduced by a factor of two.
Switch on resistance has been reduced by 30%. Switch tran-
sition times have been slowed to reduce EMI generation.
The oscillator frequency has been reduced to 200kHz to
maintain high efficiency over a wide output current range.
The pinout has been changed to improve PC layout by
allowing the high current high frequency switching cir-
cuitry to be easily isolated from low current noise sensitive
control circuitry. The new SO-8 package includes a fused
ground lead which significantly reduces the thermal resis-
tance of the device to extend the ambient operating tem-
perature range. There is an optional function of shutdown
or synchronization. Standard surface mount external parts
can be used including the inductor and capacitors.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Portable Computers
Battery-Powered Systems
Battery Charger
Distributed Power
TYPICAL APPLICATION
Efficiency vs Load Current
5V Buck Converter
INPUT
6V TO 25V
C3*
10µF TO
50µF
100
95
EFFICIENCY (%)
90
85
80
75
70
V
OUT
= 5V
V
IN
= 10V
L = 33µH
+
V
IN
BOOST
C2
0.33µF
V
SW
L1**
15µH
D2
1N914
OUTPUT**
5V, 1.25A
LT1576
OPEN = ON
SHDN
GND
V
C
BIAS
FB
D1
1N5818
C
C
100pF
R1
15.8k
R2
4.99k
* RIPPLE CURRENT RATING
≥
I
OUT
/2
** INCREASE L1 TO 30µH FOR LOAD
CURRENTS ABOVE 0.6A AND TO
60µH ABOVE 1A
SEE APPLICATIONS INFORMATION
+
C1
100µF, 10V
SOLID
TANTALUM
1576 TA01
U
0
0.25
0.50 0.75 1.00
LOAD CURRENT (A)
1.25
1.50
1576 TA02
U
U
1
LINER [ LINEAR TECHNOLOGY ]
