NATIONAL SEMICONDUCTOR ANNOUNCES HIGH-PRECISION CURRENT GAUGE ICs WITH DIRECT DIGITAL OUTPUT

August 10, 1998 - National Semiconductor Corporation® today introduced a pair of high-precision current gauge ICs for use in battery fuel monitors, motion control diagnostics and load current sensing of power sources. The LM3812 and LM3813 current gauges feature a patented 4-milliohm internal lead frame resistor that produces near-zero insertion losses, eliminating the need for external sense elements. Near-zero insertion losses from current flow measurements are particularly important when measuring currents in the ampere range.

The LM3812 senses current on the positive side of the load, while the LM3813 is used for low-side current sensing. Both devices measure current flow with virtually zero insertion loss in the measurement line. In turn, they send a highly accurate pulse width modulated (PWM) digital output directly to a microcontroller, indicating current magnitude and direction. PWM accuracy at room temperature is rated at ?2%.

"Other current measurement devices have an analog output that must be converted to digital information when interfacing to a microcontroller," said Venkatesh Shan, National's director of marketing for power management products. "In contrast, National's solution simplifies the design, lowers cost, and eliminates measurement errors caused by amplifier offset as well as value tolerances of external resistors required by competing devices."

The voltage across the lead frame resistor is measured with a delta-sigma converter, then converted to a PWM output that is universally compatible with all microcontrollers. The advantage of a delta-sigma converter is its inherent ability to cancel the sensor's input offset voltage, the largest contributor of measurement error when sensing voltages in the microvolt range.

Both devices can be set at the factory in one of two current options, either -1A to +1A or -7A to +7A. Two modes of operation are also available: In precision mode, current is averaged over a 50msec time period. In fast mode, current is averaged over a 6msec time period, providing immunity to current spikes. This type of filtering would be impossible to accomplish on an IC with analog components.

Price and Availability The LM3812 and LM3813 are currently available in 8-pin SOIC packages and are priced at $1.52 each when purchased in 1,000-unit lots.

For more information on the LM3812 and LM3813, visit our website at http://www.national.com 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 http://www.national.com

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