NATIONAL SEMICONDUCTOR INTRODUCES HIGH-PRECISION CURRENT SENSORS FOR FUEL GAUGING IN CELL PHONES AND BATTERY-POWERED HANDHELD DEVICES

August 28, 2000- National Semiconductor Corporation (NYSE:NSM) today announced a pair of high-precision current gauge ICs that are ideal for monitoring battery capacity in cellular phones, information appliances, and other small portable devices. Housed in MSOP-8 packages - the smallest available - the trim LM3822 and LM3824 current sensors are also ideal for applications requiring motion control diagnostics or load current sensing of power sources.

"As cell phones and handheld devices incorporate more and more functions, customers require accurate displays of remaining run-time," said Steven Hunt, manager of marketing and applications for National's Portable Power Systems Group. "And since the LM3822 and LM3824 are the smallest, most accurate current sense ICs in the market, they will be key components in allowing vendors to integrate this key feature in new battery-powered products."

National's breakthrough current sensor design can be attributed to the integration of a unique internal sense resister with low insertion losses and an integrated delta-sigma converter that eliminates offset error, especially when sensing small currents. Like other members of National's current-gauge family, the LM3822/24 sensors feature National's patented 3-milliohm internal lead frame resistor. Its low resistance value produces near-zero insertion losses, while eliminating the need for external sense elements. In addition, the LM3822/24 sensors' output is a highly accurate pulse width modulated (PWM) digital signal that is universally compatible with all microcontrollers. The PWM accuracy of the LM3822/24 at room temperature is rated at ?2%. An analog output is also possible with the addition of a simple R-C filter or an external op-amp filter.

The integrated delta-sigma converter, used to measure voltage across the lead frame resistor, has the inherent ability to cancel out the sensor's input offset voltage, which is the largest contributor to measurement error in the microvolt range. A ?2% full scale accuracy at room temperature gives it an advantage over an analog amplifier, especially at sense currents in the range of 0.05 to 0.1 times the full scale current.

Both ICs sense magnitude and direction of current in two ranges:-1.0A to +1.0A or -2.0A to +2.0A. Two modes of operation are available. The LM3822 operates in precision mode, averaging current over a 50msec time period at 0.1% PWM resolution, while providing immunity to current spikes. The LM3824 operates in high-speed mode, with current averaged over a 6msec time period at 0.8% PWM resolution.

Price and Availability
The LM3822 and LM3824 are currently available in 8-pin MSOP packages and are priced at $1.20 each when purchased in 1,000-unit lots. For more information on the LM3822 and LM3824, visit National's World Wide Web site at http://www.national.com/pf/LM/LM3822.html and http://www.national.com/pf/LM/LM3824.html.

About National Semiconductor
National Semiconductor provides system-on-a-chip solutions for the information age. Combining real-world analog and state-of the-art digital technology, the company's chips lead many sectors of the personal computer, communications, and consumer markets. With headquarters in Santa Clara, California, National reported sales of $2.1 billion for its last fiscal year and has about 10,500 employees worldwide. Additional company and product information is available on the World Wide Web at www.national.com.