LM2650
Synchronous Step-Down DC/DC Converter
General Description
The LM2650 is a step-down DC/DC converter featuring high
efficiency over a 3A to milliamperes load range. This feature
makes the LM2650 an ideal fit in battery-powered applica-
tions that demand long battery life in both run and standby
modes.
The LM2650 also features a logic-controlled shutdown mode
in which it draws at most 25μA from the input power supply.
The LM2650 employs a fixed-frequency pulse-width modu-
lation (PWM) and synchronous rectification to achieve very
high efficiencies. In many applications, efficiencies reach
95%+ for loads around 1A and exceed 90% for moderate to
heavy loads from 0.2A to 2A.
A low-power hysteretic or
″
sleep
″
mode keeps efficiencies
high at light loads. The LM2650 enters and exits sleep mode
automatically as the load crosses
″
sleep in
″
and
″
sleep out
″
thresholds. The LM2650 provides nodes for programming
both thresholds via external resistors.Alogic input allows the
user to override the automatic sleep feature and keep the
LM2650 in PWM mode regardless of the load level.
An optional soft-start feature limits current surges from the
input power supply at start up and provides a simple means
of sequencing multiple power supplies.
Features
n
Ultra high efficiencies (95% possible)
n
High efficiency over a 3A to milliamperes load range
n
Synchronous switching of internal NMOS power FETs
n
Wide input voltage range (4.5V to 18V)
n
Output voltage adjustable from 1.5V to 16V
n
Automatic low-power sleep mode
n
Logic-controlled micropower shutdown (I
QSD
≤
25 μA)
n
Frequency adjustable up to 300 kHz
n
Frequency synchronization with external signal
n
Programmable soft-start
n
Short-circuit current limiting
n
Thermal shutdown
n
Available in 24-lead Small-Outline package
Applications
n
Notebook and palmtop personal computers
n
Portable data terminals
n
Modems
n
Portable Instruments
n
Global positioning devices (GPSs)
n
Battery-powered digital devices
Typical Application
DS012848-1
Converting a Four-Cell Li Ion Battery to 5V
LM2650-ADJ Efficiency
DS012848-2
November 2000
L
2000 National Semiconductor Corporation
DS012848
www.national.com