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Sep 28, 1998

September 28, 1998 - National Semiconductor Corporation? today announced a low-voltage, high-efficiency step-up (boost) DC-DC switching power regulator that addresses the size and power needs of the portable electronic equipment market. The LM2621 is specially designed for voltage regulation for loads up to 1A, such as those found in cellular phones, pagers, handheld information appliances, PDAs, laptop and portable computers. Housed in an 8-pin MSOP (Mini Small Outline Package), the device requires only half the board space of similar regulators in standard SO (Small Outline) packages. Additional reductions in board space result from the LM2621's high switching frequency, adjustable up to 2MHz, which allows the use of smaller surface-mount inductors and capacitors in the circuit.

"A proprietary constant-duty cycle gated oscillator topology assures high efficiency over a wide load range," said Luc Van de Perre, National's power management marketing manager. "In addition, the 2MHz switching frequency allows the smallest solution (0.35 sq. inch) available at this power level."

National's new IC combines a switching controller, N-channel power MOSFET, built-in peak switch current limit, thermal limit and voltage reference on one chip. The LM2621's gated oscillator control scheme uses an internal 0.17 Ohm N-Channel MOSFET switch and a hysteresis window to accurately regulate the output voltage. The low Rds-on switch makes it possible to have a 1A load current in a small MSOP-8 package. A second advantage of the control scheme is that quiescent current is inherently very low, typically 80 microA. At light loads, efficiency is as much as 10% higher than conventional PWM control schemes and there are no stability issues. Efficiencies of up to 90% are common.

Input supply voltages can vary from 1.2V to 14V, while output voltages can be adjusted between 1.24V and 14V. The device will start from an input as low as 1.1V and will continue to operate down to 0.65V.

A power-saving shutdown mode extends battery life by reducing the total quiescent current to less than a guaranteed 2.5 microA over temperature. Protection circuitry includes cycle-by-cycle peak current limit and thermal shutdown that disables the MOSFET power switch when the junction temperature exceeds 160 degrees C.

The LM2621 can also be used as a SEPIC (buck-boost) converter. In this configuration, for example, it will supply a regulated 3.3V output from a 1-cell Li-Ion battery supply (2.5V to 4.2V), which is a very common battery source in cellular phones and portable consumer electronic appliances.

Price and Availability
The LM2621MM is available in National's 8-pin MSOP, and is priced at $1.90 each when purchased in quantities of 1000.

For more information on the LM2621, visit our website at http://www.national.com/pf/LM/LM2621.html.

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.