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
s Portable Computers
s Battery-Powered Systems
s Battery Chargers
s Distributed Power Systems
1.5A, 200kHz Step-Down
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.
5V TO 15V C3* +
3.3V Buck Converter
OPEN = ON
* RIPPLE CURRENT RATING ≥ IOUT/2
** INCREASE L1 TO 30µH FOR LOAD
CURRENTS ABOVE 0.6A AND TO
60µH ABOVE 1A
SEE APPLICATIONS INFORMATION
Efficiency vs Load Current
VOUT = 3.3V
VIN = 5V
L = 25µH
0.25 0.50 0.75 1.00
LOAD CURRENT (A)