1FEATURES

2• 200 kHz Fixed-Frequency Switching

• Switching Synchronization with an External

Signal up to 400 kHz

• Optional Pulse-Skipping Mode

• Adjustable Secondary Feedback

• Input Undervoltage Lockout

• Output Undervoltage Shutdown Protection

• Output Overvoltage Shutdown Protection

• Programmable Soft-Start (Each Controller)

• 5V, 50 mA Linear Regulator Output

• Precision 2.5V Reference Output

• 28-Pin Package

APPLICATIONS

• Notebook and Subnotebook Computers

• Wireless Data Terminals

• Battery-Powered Instruments

KEY SPECIFICATIONS

• 96% Efficient

• 5.5V to 30V Input Range

• Dual Outputs Adjustable from 2.2V to 6V

• 0.5% Typical Load Regulation Error

• 0.002%/V Typical Line Regulation Error

DESCRIPTION

The LM2640 is a dual step-down power supply

controller intended for application in notebook

personal computers and other battery-powered

equipment.

Fixed-frequency synchronous drive of logic-level N-

channel power MOSFETs is combined with an

optional pulse-skipping mode to achieve ultra efficient

power conversion over a 1000:1 load current range.

The pulse-skipping mode can be disabled in favor of

fixed-frequency operation regardless of the load

current level.

High DC gain and current-mode feedback control

assure excellent line and load regulation and a wide

loop bandwidth for fast response to dynamic loads.

An internal oscillator fixes the switching frequency at

200 kHz. Optionally, switching can be synchronized

to an external clock running as fast as 400 kHz.

An optional soft-start feature limits current surges

from the input power supply at start up and provides a simple means of start-up sequencing.

Logic-level inputs allow the controllers to be turned

ON and OFF separately.