NATIONAL SEMICONDUCTOR ANNOUNCES INDUSTRY'S SMALLEST DUAL SYNCHRONOUS STEP-DOWN POWER CONTROLLER FOR PORTABLE PC SYSTEMS

High-Efficiency Device Combines Two Separate Voltage Controllers, Linear Regulator and Precision Reference on a Single Chip

May 19, 1998 - National Semiconductor Corporation? today announced a high-efficiency synchronous step-down power controller with dual adjustable outputs as part of a complete 2-chip solution for supplying system voltages to portable PCs. The LM2640 output voltages, adjustable between 2.2V and 6V, are typically set at 5V and 3.3V. In addition, the new device features an integrated 5V/50mA linear regulator and a 2.5V precision reference. The 5V linear regulator operates as a system back-up voltage, remaining on even when the dual synchronous controllers and 2.5V reference are shut down.

"By pairing the dual LM2640 with National's LM2630 controller, we now provide all the blocks needed for forward integrating a complete notebook computer power supply," said Venkatesh Shan, National's director of marketing for power management products. "In addition, the LM2640 contains all the core blocks needed for system power supply for a multiple-voltage portable systems."

Like the companion LM2630, the LM2640 is housed in a space-saving, ultra-thin package that occupies just 6 X 6 mm2 of board space, making it ideal for battery-powered systems, such as wireless data terminals handheld instruments, PDAs and mobile communications, where board space is at a premium.

National's LM2640 takes advantage of the highest performance N-channel MOSFET technology available today to achieve high output current. In typical 3A applications, efficiencies of 92% and greater are common. Under light load conditions, the device uses a pulse-skipping mode to increase efficiencies over a 1,000:1 load current range.

The LM2640's high performance can also be attributed to a current-mode feedback control scheme that quickly achieves output voltage with fast loop response. Superior line regulation has typical error rate of just 0.002%/V. Load regulation is a low 0.5%.

Protection circuitry includes programmable soft-start, thermal shutdown, undervoltage and overvoltage latch-off, cycle-by-cycle current limit and latch-off current limits.

Input supply voltages can vary from 5.5V to 30V, making the LM2640 compatible with most currently used battery chemistries. An internal oscillator fixes the switching frequency at 200kHz. As an option, switching can be synchronized to an external clock running up to 400kHz.

Price and Availability
The LM2640MTC is offered in National's 28-pin TSSOP, and is priced at $4.50 each when purchased in quantities of 1000.

For more information on the LM2640, visit our website at http://www.national.com/pf/LM/LM2640.html or contact National's Customer Response Group at 1-800-272-9959.

National Semiconductor Corporation produces system-on-a-chip silicon solutions for the information highway, based on its leadership in analog and mixed signal technologies. National is headquartered in Santa Clara, California, and focuses on the communications, personal systems and consumer markets. National has annual sales of approximately $2.5 billion and 13,000 employees worldwide. Additional company and product information is available on the World Wide Web at www.national.com.