Carrollton, Texas-based Benchmarq Microelectronics Inc is shipping what it claims is the first integrated system for comprehensive battery capacity monitoring that meets the Intel Corp-Duracell Inc System Management Bus and Smart Battery Data specification. The bq2040 is available OEM or to battery value-added resellers wanting to develop Smart Battery packs based on the SMBus specification. The product is based on Benchmarq’s patented battery capacity monitoring technology and the bq2040 is available for use with Nickel Cadmium, Nickel Metal Hydride and Lithium Ion batteries. The bq2040 communicates milliAmps hour capacity indication as well as other battery management information using the SMBus or may directly display the battery capacity information using five light emitting diodes. It is packaged in a small, 16-pin, 150-mil surface mounted circuit and, together with the necessary external components, can occupy less than half a square inch of the board, enabling easy battery pack integration, says the company. Benchmarq says the bq2040 eliminates the need for an external thermistor or resonator. It has a battery capacity monitor that measures the voltage drop across a very small-value sense resistor connected in series with the negative battery terminal, enabling both charge and discharge current sensing. An internal temperature-compensated clock provides the necessary time-base stability across voltage and temperature without the need for external components such as a crystal or other passive components. The bq2040 uses an internal temperature sensor that yields battery temperature in 0.1oK steps across a wide range from less than minus 40oC to greater than 85oC. This provides a wide temperature range for internal compensations and significantly reduces the number of external components placed in a battery pack, according to the company. Because self-discharge is a significant component of capacity removed from a battery, the bq2040 adjusts the available battery capacity for the amount of self-discharge based on the amount of storage time at various temperatures, amount of available charge, and type of battery in use. The bq2040 automatically integrates the charge and discharge currents of a rechargeable battery over a wide, dynamic range to adjust for the battery inefficiencies at various loads, charge rates and temperatures. With a current measurement dynamic range greater than 500-to-1, the bq2040 meets the current range requirements of portable computers, cellular phones and other portable electronic equipment. The device also monitors battery terminal characteristics to provide end-of-discharge voltage detection and a means for detecting battery replacement and battery wear-out. An external electrically erasable, programmable ROM stores battery initialisation information, or data can be transferred externally to the bq2040 on-chip nonvolatile RAM. The bq2040 is small enough to fit in the crevice between two A cells, simplifying integration into the battery pack. Samples and development kits will be available in November. Initial production quantities are expected in January 1995. Pricing for the 16-pin, 150-mil SOIC is less than $5 in OEM quantities. The EV2040 development kit costs $150.
