January 2005
LM2675
SIMPLE SWITCHER® Power Converter High Efficiency
1A Step-Down Voltage Regulator
To simplify the LM2675 buck regulator design procedure,
there exists computer design software, LM267X Made
Simple version 6.0.
General Description
The LM2675 series of regulators are monolithic integrated
circuits built with a LMDMOS process. These regulators
provide all the active functions for a step-down (buck)
switching regulator, capable of driving a 1A load current with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5.0V, 12V, and an
adjustable output version.
Features
n Efficiency up to 96%
n Available in SO-8, 8-pin DIP and LLP packages
n Computer Design Software LM267X Made Simple
(version 6.0)
Requiring a minimum number of external components, these
regulators are simple to use and include patented internal
frequency compensation (Patent Nos. 5,382,918 and
5,514,947) and a fixed frequency oscillator.
n Simple and easy to design with
n Requires only 5 external components
n Uses readily available standard inductors
n 3.3V, 5.0V, 12V, and adjustable output versions
n Adjustable version output voltage range: 1.21V to 37V
The LM2675 series operates at a switching frequency of
260 kHz, thus allowing smaller sized filter components than
what would be needed with lower frequency switching regu-
lators. Because of its very high efficiency ( 90%), the cop-
per traces on the printed circuit board are the only heat
sinking needed.
n
1.5% max output voltage tolerance over line and load
conditions
>
n Guaranteed 1A output load current
n 0.25Ω DMOS Output Switch
n Wide input voltage range: 8V to 40V
n 260 kHz fixed frequency internal oscillator
n TTL shutdown capability, low power standby mode
n Thermal shutdown and current limit protection
A family of standard inductors for use with the LM2675 are
available from several different manufacturers. This feature
greatly simplifies the design of switch-mode power supplies
using these advanced ICs. Also included in the datasheet
are selector guides for diodes and capacitors designed to
work in switch-mode power supplies.
Typical Applications
Other features include a guaranteed 1.5% tolerance on
output voltage within specified input voltages and output
load conditions, and 10% on the oscillator frequency. Ex-
ternal shutdown is included, featuring typically 50 µA
stand-by current. The output switch includes current limiting,
as well as thermal shutdown for full protection under fault
conditions.
>
n Simple High Efficiency ( 90%) Step-Down (Buck)
Regulator
n Efficient Pre-Regulator for Linear Regulators
n Positive-to-Negative Converter
Typical Application
01280301
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.
Windows® is a registered trademark of Microsoft Corporation.
© 2005 National Semiconductor Corporation
DS012803
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