LM2678 SIMPLE SWITCHER High Efficiency 5A Step-Down Voltage Regulator
May 1, 2008
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 characteristics.
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 adjustable
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%
tolerance.
Features
■
Efficiency up to 92%
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Simple and easy to design with (using off-the-shelf
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external components)
120 mΩ DMOS output switch
3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
50μA
standby current when switched OFF
±2%maximum output tolerance over full line and load
conditions
Wide input voltage range: 8V to 40V
260 KHz fixed frequency internal oscillator
−40 to +125°C operating junction temperature range
Applications
■
Simple to design, high efficiency (>90%) step-down
switching regulators
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Efficient system pre-regulator for linear voltage regulators
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Battery chargers
Typical Application
10088603
SIMPLE SWITCHER
®
is a registered trademark of National Semiconductor Corporation
© 2008 National Semiconductor Corporation
100886
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
