LM2670 SIMPLE SWITCHER High Efficiency 3A Step-Down Voltage Regulator with Sync
August 1998
LM2670
SIMPLE SWITCHER
®
High Efficiency 3A Step-Down
Voltage Regulator with Sync
General Description
The LM2670 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
3A 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.
The switching clock frequency can be provided by an inter-
nal fixed frequency oscillator (260KHz) or from an externally
provided clock in the range of 280KHz to 400Khz which al-
lows the use of physically smaller sized components. A fam-
ily of standard inductors for use with the LM2670 are avail-
able from several manufacturers to greatly simplify the
design process. The external Sync clock provides direct and
precise control of the output ripple frequency for consistent
filtering or frequency spectrum positioning.
The LM2670 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.
Features
n
Efficiency up to 94%
n
Simple and easy to design with (using off-the-shelf
external components)
n
150 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
External Sync clock capability (280KHz to 400KHz)
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
n
Communications and radio equipment regulator with
synchronized clock frequency
Typical Application
DS100942-3
SIMPLE SWITCHER
®
is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS100942
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
