LT1578/LT1578-2.5
1.5A, 200kHz Step-Down
Switching Regulator
FEATURES
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DESCRIPTIO
1.5A Switch Current
High Efficiency鈥擫ow Loss 0.2鈩?Switch
Constant 200kHz Switching Frequency
4V to 15V Input VoltageRange
Minimum Output: 1.21V
Low Supply Current: 1.9mA
Low Shutdown Current: 20碌A
Easily Synchronizable Up to 400kHz
Cycle-by-Cycle Current Limit
Reduced EMI Generation
Low Thermal Resistance SO-8 Package
Uses Small Low Value Inductors
The LT
廬
1578 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 LT1578 is a modified version of the
LT1507 that has been optimized for noise sensitive appli-
cations. It will operate over a 4V to 15V input range.
In addition, the reference voltage has been lowered to al-
low 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 al-
lowing the high current, high frequency switching circuitry
to be easily isolated from low current, noise sensitive con-
trol circuitry. The new SO-8 package includes a fused
ground lead that significantly reduces the thermal resistance
of the device to extend the ambient operating temperature
range. 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 Chargers
Distributed Power Systems
TYPICAL APPLICATION
Efficiency vs Load Current
3.3V Buck Converter
INPUT
5V TO 15V
C3*
10碌F TO
50碌F
90
85
+
V
IN
BOOST
C2
0.33碌F
V
SW
EFFICIENCY (%)
L1**
15碌H
D2
1N914
OUTPUT**
3.3V, 1.25A
80
75
70
65
60
55
50
0
0.25
0.50 0.75 1.00
LOAD CURRENT (A)
1.25
1.50
V
OUT
= 3.3V
V
IN
= 5V
L = 25碌H
LT1578
OPEN = ON
SHDN
GND
FB
V
C
C
C
100pF
D1
1N5818
R1
8.66k
R2
4.99k
* RIPPLE CURRENT RATING
鈮?/div>
I
OUT
/2
** INCREASE L1 TO 30碌H FOR LOAD
CURRENTS ABOVE 0.6A AND TO
60碌H ABOVE 1A
SEE APPLICATIONS INFORMATION
+
C1
100碌F, 10V
SOLID
TANTALUM
1578 TA01
U
1578 TA02
U
U
1
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