FEATURES
s Constant 200kHz Switching Frequency
s 1.21V Reference Voltage
s Fixed 5V Output Option
s Easily Synchronizable
s Uses All Surface Mount Components
s Inductor Size Reduced to 15µH
s Saturating Switch Design: 0.2Ω
s Effective Supply Current: 1.16mA
s Shutdown Current: 20µA
s Cycle-by-Cycle Current Limiting
s Fused Lead SO-8 Package
U
APPLICATIO S
s Portable Computers
s Battery-Powered Systems
s Battery Charger
s Distributed Power
LT1576/LT1576-5
1.5A, 200kHz Step-Down
Switching Regulator
DESCRIPTIO
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.
TYPICAL APPLICATION
5V Buck Converter
INPUT
6V TO 25V C3* +
10µF TO
50µF
C2
0.33µF
VIN BOOST
VSW
LT1576 BIAS
L1**
15µH
D2
1N914
OUTPUT**
5V, 1.25A
OPEN = ON
SHDN
GND
* RIPPLE CURRENT RATING ≥ IOUT/2
** INCREASE L1 TO 30µH FOR LOAD
CURRENTS ABOVE 0.6A AND TO
60µH ABOVE 1A
SEE APPLICATIONS INFORMATION
FB
VC
CC
100pF
D1
1N5818
R1
15.8k
R2 +
4.99k
C1
100µF, 10V
SOLID
TANTALUM
1576 TA01
Efficiency vs Load Current
100
VOUT = 5V
95
VIN = 10V
L = 33µH
90
85
80
75
70
0
0.25 0.50 0.75 1.00
LOAD CURRENT (A)
1.25 1.50
1576 TA02
1
