LT1375/LT1376
1.5A, 500kHz Step-Down
Switching Regulators
FEATURES
s Constant 500kHz Switching Frequency
s Easily Synchronizable
s Uses All Surface Mount Components
s Inductor Size Reduced to 5µH
s Saturating Switch Design: 0.4Ω
s Effective Supply Current: 2.5mA
s Shutdown Current: 20µA
s Cycle-by-Cycle Current Limiting
U
APPLICATIO S
s Portable Computers
s Battery-Powered Systems
s Battery Charger
s Distributed Power
DESCRIPTIO
The LT®1375/LT1376 are 500kHz monolithic buck mode
switching regulators. A 1.5A switch is included on the die
along with all the necessary oscillator, control and logic
circuitry. High switching frequency allows a considerable
reduction in the size of external components. The topology
is current mode for fast transient response and good loop
stability. Both fixed output voltage and adjustable parts are
available.
A special high speed bipolar process and new design
techniques achieve high efficiency at high switching fre-
quency. Efficiency is maintained over a wide output cur-
rent range by using the output to bias the circuitry and by
utilizing a supply boost capacitor to saturate the power
switch. A shutdown signal will reduce supply current to
20µA on both parts. The LT1375 can be externally syn-
chronized from 550kHz to 1MHz with logic level inputs.
The LT1375/LT1376 fit into standard 8-pin PDIP and SO
packages, as well as a fused lead 16-pin SO with much
lower thermal resistance. Full cycle-by-cycle short-cir-
cuit protection and thermal shutdown are provided.
Standard surface mount external parts are used, includ-
ing the inductor and capacitors.
For low input voltage applications with 3.3V output, see
LT1507. This is a functionally identical part that can
operate with input voltages between 4.5V and 12V.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
5V Buck Converter
INPUT
6V† TO 25V C3* +
10µF TO
50µF
DEFAULT
= ON
BOOST
VIN VSW
LT1376-5 BIAS
SHDN
GND
FB
VC
CC
3.3nF
D2
1N914
C2
0.1µF
L1**
5µH
OUTPUT**
5V, 1.25A
D2
1N5818
+ C1
100µF, 10V
SOLID
TANTALUM
* RIPPLE CURRENT ≥ IOUT/2
** INCREASE L1 TO 10µH FOR LOAD CURRENTS ABOVE 0.6A AND TO 20µH ABOVE 1A
† FOR INPUT VOLTAGE BELOW 7.5V, SOME RESTRICTIONS MAY APPLY.
SEE APPLICATIONS INFORMATION.
1375/76 TA01
Efficiency vs Load Current
100
VOUT = 5V
VIN = 10V
90 L = 10µH
80
70
60
50
0
0.25 0.50 0.75 1.00
LOAD CURRENT (A)
1.25
1375/76 TA02
1
