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How to manage power on the go
December 16, 1996
5 Min Read
Newton, MA--As portable applications continue to expand, designers must find better ways to manage power, conserve energy, and improve product performance. Some of the latest designs bring that goal much closer by achieving more efficient and better-managed power usage. Here's how they work.
Gauge and charger support SMBus and SMData specs
The bq2091 Gas Gauge IC from Benchmarq Microelectronics Inc., Dallas, TX, directly supports capacity monitoring for NiCd, NiMH, and Li-Ion battery chemistries. The IC uses the System Management Bus (SMBus) protocol that supports many Smart Battery Data (SBData) commands and charge controls.
Battery state-of-charge, capacity remaining, remaining time, and chemis-try are available over the serial link. A four-segment LED display graphic-ally depicts battery full-to-empty in 25% increments.
Packaged in a small, 16-pin, 150-mil SOIC, the bq2091, with the necessary external components, occupies less than 0.8 sq. inch on a pc board. The device also eliminates the need for an external thermistor or resonator. It fits in the crevice between two A cells, simplifying integration into the battery pack.
Another recent release, said to be the first of its kind, is Benchmarq's DV2043S7 Level 2 Smart Charger. The system features a Smart Battery selector that automatically switches system power to dc when available, and switches power between the two battery packs when a battery is removed from the system. It supports stand-alone or system-control charging of one or two battery packs.
About the size of a credit card, the DV2043S7 incorporates a Benchmarq bq2054 Gas Gauge IC and a microcontroller for high-efficiency, low-ripple, switch-mode design with high-sidecurrent sensing. The system complies with release 1.0 of the SMBus, the Level 2 Smart Charger, and the Smart Bat-tery Selector specifications.
"Portable computer manufacturers may want to use the SMBus and Smart Battery data without locking themselves into a single battery supplier or limiting battery-pack configurations," says Bill Bentley, product marketing manager at Benchmarq. "With the bq2091 and the DV2043S7, companies can implement a complete charger/fuel gauge sys-tem, allowing them to pursue multiple suppliers and battery technologies for their systems."
ICs monitor battery power
To simplify the design of portable products such as computer and consumer equipment, Motorola's Semiconductor Products Sector, Phoenix, AZ, has introduced three complete families of CMOS power-management ICs for battery-powered applications.
The first family, MC33463 and MC33466 series micropower switching voltage regulators, available with 3.0, 3.3, and 5.0V options, come in three-pin SOT-89 packages with an on-chip switch transistor or provisions for an external switch.
The MC33463 variable-frequency-modulation controllers have a quiescent bias current (IQ) of 4 muA; the MC33466 fixed-frequency pulse-width-modula-tion switchers have a quiescent current of 15 muA.
The second family, three series of CMOS micropower linear regula-tors (MC78LCxx, MC78FCxx, and MC78BCxx), have ultra-low IQ. Designed for cameras, camcorders, VCRs, and hand-held communications products, the regulators have voltage options of 3.0, 3.3, 4.0, and 5.0V. The MC78LCxx series has an 80-mA output current and a dropout voltage of 0.7V at 40 mA in SOT-23 or SOT-89 packages. The MC78FCxx series has an output current of 120 mA, dropout of 0.2V, and a SOT-89 package. The MC78BCxx series comes in aSOT-23 package for use with an external power transistor for higher output currents.
The company's third new family, MC33464 and MC33465 micro-power undervoltage sensing ICs directly monitor MPU/logic power supplies in portable, appliance, automotive, and industrial equipment. Both series come with threshold voltages of 0.9, 2.0, 2.7, 3.0, and 4.5V. The user has a choice of open-drain or complimentary CMOS reset output configurations.
The MC33464 series has a low quiescent current of 0.8 muA in SOT-23 or SOT-89 packages. The MC33465 series adds programmable, time-delayed output with a quiescent current of 1.0 muA in a SOT-23 package.
Comparators deliver low supply voltage, low current,
and small size
With any device targeted for portable applications, power consumption be-comes critical. With that in mind, National Semiconductor, Santa Clara, CA, has introduced TinyPakTM LMC7215 and LMC7225 CMOS comparators. The devices combine rail-to-rail input stages and a low supply current of about 0.7muA over a 2 to 8V supply-voltage range. "A low supply current is important to extend battery life," says Jim Chase, technical marketing program manager. "These comparators' current is less than any other device's in their class."
In order to bring flexibility to power supervision and analog conditioning, both de-vices reside in TinyPak SOT-23 packages, enabling easy integration into designs. Among the products they help supervise: laptop computers, cellular phones, metering systems, hand-held electronics, and alarm and monitoring circuits.
The LMC7215 features a push-pull output stage that allows operation with a minimum amount of power consumption when driving any load. Open-drain outputs on the LMC7225 enable designers to optimize mixed-voltage system designs. With them, designers can connect an external resistor to use the output as a level shifter to voltages up to 15V.
Other notable features of the comparators: an input common-mode voltage that exceeds supply voltage for systems that monitor large input signals or operate from single supplies, and a minimum operating voltage of 2V for systems with low voltages or multiple supply voltages.
"With our devices, designers get the lowest supply-voltage operation at the lowest supply current in the smallest package," says Chase, "without having to resort to less optimal op-amp implementations."
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