LT1578-2.5_15 Datasheet, PDF (1/28 Pages) Linear Technology – 1.5A, 200kHz Step-Down Switching Regulator

FEATURES
s _{1.5A Switch Current}
s _{High Efficiency—Low Loss 0.2Ω Switch}
s Constant 200kHz Switching Frequency
s _{4V to 15V Input VoltageRange}
s _{Minimum Output: 1.21V}
s _{Low Supply Current: 1.9mA}
s _{Low Shutdown Current: 20µA}
s _{Easily Synchronizable Up to 400kHz}
s _{Cycle-by-Cycle Current Limit}
s _{Reduced EMI Generation}
s _{Low Thermal Resistance SO-8 Package}
s _{Uses Small Low Value Inductors}
U
APPLICATIO S
s _{Portable Computers}
s _{Battery-Powered Systems}
s _{Battery Chargers}
s _{Distributed Power Systems}
LT1578/LT1578-2.5
1.5A, 200kHz Step-Down
Switching Regulator
DESCRIPTIO
The LT^®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.
TYPICAL APPLICATION
INPUT
5V TO 15V _{C3* +}
10µF TO
50µF
3.3V Buck Converter
C2
0.33µF
V_IN BOOST
V_SW
LT1578
L1**
15µH
D2
1N914
OUTPUT**
3.3V, 1.25A
OPEN = ON
SHDN
GND
* RIPPLE CURRENT RATING ≥ I_OUT/2
** INCREASE L1 TO 30µH FOR LOAD
CURRENTS ABOVE 0.6A AND TO
60µH ABOVE 1A
SEE APPLICATIONS INFORMATION
FB
V_C
C_C
100pF
D1
1N5818
R1
8.66k
R2 ⁺
4.99k
C1
100µF, 10V
SOLID
TANTALUM
1578 TA01
Efficiency vs Load Current
90
85
80
75
70
65
60
55
50
0
V_OUT = 3.3V
V_IN = 5V
L = 25µH
0.25 0.50 0.75 1.00
LOAD CURRENT (A)
1.25 1.50
1578 TA02
1