SAN JOSE, CALIF. Three hot new supervisor ICs from Micrel, PowerSmart and Unitrode show the innovative routes vendors are taking to achieve higher measurement accuracies in battery management. The latest ICs eliminate battery chatter during the charge-discharge process, double-check the accuracy of battery measurements as they pass over a system and check the parameters of some of the lesser-discussed primary-cell lithium chemistries.
Micrel, based here, for instance, designed its MIC2778 voltage supervisor IC with adjustable hysteresis to eliminate battery chatter, which complicates charge-discharge cycling. "Most battery-powered systems disconnect the battery from the load when it discharges to a certain level. With the load removed, battery voltage tends to increase slightly, making the system believe that the battery has been recharged," said product marketing manager Jim Judkins. "The subsequent decrease when load is reestablished can cause chatter without sufficient hysteresis."
With the MIC2778, trip points and hysteresis are separately adjusted with external resistors, allowing for last-minute changes in field testing and allowing OEMs to stock a single device rather than customized parts. Nominal supply current is 1 microamp. Two product grades are offered: the 2778-1, with a guaranteed accuracy of plus/minus 1 percent, and the -2 version at plus/minus 2 percent. The BiCMOS part comes in the company's IttyBitty SOT23-5 package. The MIC2778-2BM5 is 78 cents each in lots of 1,000.
The PS331 smart-battery IC from PowerSmart (Shelton, Conn.) is said to be the first device in volume production that enables data error checking. The CMOS device meets the packet error checking specs of the System Management Bus Specification version 1.1, predicting remaining battery capacity of any chemistry to within 1 percent. A host device appends a packet error code at the end of each message transfer, to check the integrity of the data communication. For each read or write bus transaction, an 8-bit cyclic redundancy check is used to calculate a frame check sequence, taking 1 ms to calcu- late a single data byte.
An integrating, self-calibrating 14-bit A/D converter measures current, voltage and temperature. An advanced 8-bit RISC microprocessor enables fast data computations.
The PS331 comes in a 28-pin single small-outline pack and costs under $4 in big quantities. An evaluation kit is $199.
For its part, Unitrode says its bq2052 Benchmarq gas-gauge IC for primary lithium cells is the first production-level chip to monitor the various parameters of lithium sulphur dioxide and lithium manganese dioxide battery packs, types in wide use in military radios, test and measurement equipment, and other military and portable applications (see photo, page 152).
The CMOS device accurately tracks battery pack voltage, temperature and remaining capacity, using an A/D converter for battery temperature and voltage measurement, and a voltage-to-frequency converter for measuring battery capacity. The IC automatically compensates remaining capacity for battery inefficiencies based on discharge rate and temperature to provide an accurate indication of the capacity left in the pack. It talks to a host system controller using a single-wire communications port, or lights a programmable LED display to indicate remaining capacity. In a 16-pin, 150-mil SOIC, the bq2052 is $3.26 in lots of 10,000.
Micrel, (408) 944-0800
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PowerSmart, (203) 925-1340
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Unitrode, (603) 424-2410
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