LM2678 SIMPLE SWITCHER High Efficiency 5A Step-Down Voltage Regulator
March 2000
LM2678
SIMPLE SWITCHER
®
High Efficiency 5A Step-Down
Voltage Regulator
General Description
The LM2678 series of regulators are monolithic integrated
circuits which provide all of the active functions for a
step-down (buck) switching regulator capable of driving up to
5A loads with excellent line and load regulation characteris-
tics. High efficiency (
>
90%) is obtained through the use of a
low ON-resistance DMOS power switch. The series consists
of fixed output voltages of 3.3V, 5V and 12V and an adjust-
able output version.
The SIMPLE SWITCHER concept provides for a complete
design using a minimum number of external components. A
high fixed frequency oscillator (260KHz) allows the use of
physically smaller sized components. A family of standard in-
ductors for use with the LM2678 are available from several
manufacturers to greatly simplify the design process.
The LM2678 series also has built in thermal shutdown, cur-
rent limiting and an ON/OFF control input that can power
down the regulator to a low 50µA quiescent current standby
condition. The output voltage is guaranteed to a
±
2% toler-
ance. The clock frequency is controlled to within a
±
11% tol-
erance.
Features
n
Efficiency up to 92%
n
Simple and easy to design with (using off-the-shelf
external components)
n
120 mΩ DMOS output switch
n
3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
n
50µA standby current when switched OFF
n
±
2%maximum output tolerance over full line and load
conditions
n
Wide input voltage range: 8V to 40V
n
260 KHz fixed frequency internal oscillator
n
−40 to +125˚C operating junction temperature range
Applications
n
Simple to design, high efficiency (
>
90%) step-down
switching regulators
n
Efficient system pre-regulator for linear voltage
regulators
n
Battery chargers
Typical Application
DS100886-3
SIMPLE SWITCHER
®
is a registered trademark of National Semiconductor Corporation.
© 2000 National Semiconductor Corporation
DS100886
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
