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. A logic 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

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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

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

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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

© 2000 National Semiconductor Corporation

DS012848

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