Makers of battery-management chips for portable electronic products are being asked to help increase battery run times, improve the precision of charging sequences, measure remaining battery life more accurately and share battery status across a network. Chip makers are facing unprecedented pressure from customers to conserve every microwatt because battery technologies have pla-teaued with respect to the energy densities and basic operating lifetimes they can deliver.
Battery-management ICs in-tegrate LDO regulators, references, error amps, logic gates and proprietary circuits. Today's offerings, which are accurate to 1 percent or better and are said to lower overall parts count by up to 50 percent, can substantially maximize battery run-time and life.
Battery-charging devices drive much of the market. "Charging is the fastest-growing segment in battery management," said Tom Szepesi, director of marketing for the power-management group at Analog Devices Inc. (Norwood, Mass.). Users can secure up to a 10 percent increase in battery run times by being able to measure end-of-charge voltage to within 1 percent.
While so-called chemistry-independent chips that charge batteries over ranges up to 35 volts are still available, including the L6902 from Lexington, Mass.-based STMicroelectronics, most IC-charger development centers on lithium-based batteries (the L6902 can be used as a preregulator with lithium-ions). Most users expect to need more lithium-ion and lithium-polymer batteries, so vendors are concentrating on those chemistries, where charging requirements are stringent. Chip makers are focusing on high charging accuracies at all temperatures and addressing multiple battery systems.
Analog Devices Inc.'s ADP3806, for example, is a complete lithium-ion battery charging IC that combines high-voltage accuracy with a constant-current controller to simplify the deployment of constant-current, constant-voltage chargers. The ADP3806 guarantees final battery voltage to within plus/minus 0.6 percent. The ADP3801 and ADP3802, when paired with an external microcontroller for charge termination, work as fast chargers for NiCd/NiMH batteries or as universal chargers for NiCd, NiMH and Li-ion batteries. Analog (Norwood, Mass.) also offers the ADP3408, a multifunction power system chip that coordinates the battery-charging function for GSM/DCS/PCS handsets.
Texas Instruments' recently released battery-management products include an SBS-based chip set for battery management. Designed for inclusion in a 3-to-4 cell Li-ion or Li-polymer battery pack, the chip set consists of the bq29311 protection IC and the bq2081 gas-gauge chip. The bq29311 protects the lithium cells and serves as the analog front end to the bq2081 via a two-line serial bus. The bq2081 is the first in a series of capacity-monitoring ICs based on TI's Cool-GG platform. The platform integrates an 8-bit RISC CPU core, two A/D converters, flash E2PROM and two communications ports. The A/D converters' high resolution permits use of a low-ohmic (10 milliohms) sense-resistor for accurate charge and discharge integration.
TI is also marketing the bq2063, an SBS-compliant gas-gauge chip that interfaces with Seiko Instruments' S-8243 battery protection IC. The Seiko Electronics Components Division (Torrance, Calif.) also recently introduced its S-8261 series of protection ICs for single-cell lithium ions. Engineers designed TI's bq2063 and the bq2081 to reduce external parts counts in protection circuits by 40 percent.
Micrel (San Jose, Calif.), known for basic battery-supervisor/voltage-monitoring chips like the MIC2755 and MIC2778, has added to its line the MIC79050, a single-cell charger that is accurate to plus/minus 0.75percent. Fairchild Semiconductor (San Jose, Calif.), with a strong power MOSFET tinge to its portfolio, has introduced FAN7563/7564 lithium-ion charger controller chips.
Accuracy is as important for general monitoring and gas gauging as it is for charging. "The challenge is to figure out how to get more than we have, and that means using data more creatively and relying more on that data," said Dave Heacock, business-line manager for battery-management products at Texas Instruments.
"Accuracy has two parts: The first is how well the device can measure. The second is how well you can model the battery to extrapolate meaningful information. We've upped accuracy in both areas," Heacock said. As a result, ICs have moved to the next level of sophistication by bringing memory on-chip, a crucial component for storing data cost- and space-effectively. The second trick to attaining high accuracy for gauging is to integrate system functions more completely, and use a sense resistor with the lowest possible ohmic-value, embedded in the chip if possible. Maxim Semiconductor (Sunnyvale, Calif.), with a substantial power management portfolio built around battery chargers and monitors, was one of the first to do both. The DS2750 from Maxim's Dallas Semiconductor unit is a gas gauge IC that incorporates both a Li-ion protection circuit and an internal 25-milliohm current-sense resistor.
Accuracy is also important in battery protection ICs," according to Jim Hill, applications engineer for ON Semiconductor (Phoenix). Again, the goal is to monitor operating voltages and currents to well within 1percent. ON Semi's new NCP802 for use in one-cell Li-based battery packs, which integrates various internal delay circuitry to minimize external component count, senses cell voltage (to within plus/minus 25 mV), charge current and discharge current and controls the state of two n-channel MOSFET switches. The switches are in series with the cell's negative terminal. During a fault condition, the NCP802 turns off one of the MOSFETs, disconnecting the battery. Also due shortly is the company's first dedicated Li-ion charger IC, the NCP1800, a controller with plus/minus 1percent accuracy that provides the required constant-current and constant-voltage control functions.
In addition to accuracy, manufacturers and customers care about a related issue, the thermal characteristics of battery-management chips. Linear Technology Corp.'s LTC1733 is a 1-amp linear lithium-ion battery charger with thermal regulation. The constant-current, constant-voltage device has an on-chip power MOSFET whose architecture eliminates the need for an external current-sense resistor. Its thermal-regulation circuitry limits the charge current and, thus, the die temperature, during high-power operation.
Linear Technology (Milpitas, Calif.) also is offering a new device for multiple battery systems, the LTC1960. The company claims the LTC1960 is the first fully integrated dual battery charger and selector with an SPI interface (for dual smart batteries) and power crisis management. A proprietary PowerPath architecture supports simultaneous charging of both batteries and will automatically switch between power sources if someone or something removes either a battery or the driving source (wall adapter). Typical battery run-times can be extended by 10 percent and charging times reduced by up to 50 percent with the chip, according to the company, which also says the LTC1960 requires only half as many external discrete components as present solutions.
Battery-management device makers are also under the gun to shrink package sizes. TI's bq2420x, which the company says is the industry's smallest charge-management IC, is designed as the core of a battery-charging circuit for spaceconstrained applications. The three-phase controller (conditioning from a small internal current source, current-limited charging from an external source and a constant-voltage end-phase accurate to plus/minus 0.5 percent) is for single lithium batteries. TI said this topology cuts heat by more than 70 percent over a traditional linear charger. It includes a current sensor and an internal MOSFET pass resistor rated for up to 500-mA charge applications. TI packages it in an eight-pin MSOP, and it needs only two external capacitors.
The Si9731DQ charger from Vishay Siliconix (Santa Clara, Calif.) is designed small to fit system microcontrollers in cell phones, personal digital assistants and other handheld appliances. It integrates a precision reference, error amp and two internal power MOSFETs in a TSSOP-16 package to provide trickle or fast charging for all common battery types. It offers constant-voltage mode charging to 4.1- or 4.2- volt lithium-ion types with 50-mV accuracy.
Allegro Microsystems Inc.
EETInfo No. 618
Analog Devices Inc.
EETInfo No. 619
EETInfo No. 620
Galaxy Power Inc.
EETInfo No. 621
Linear Technology Corp.
EETInfo No. 622
EETInfo No. 623
EETInfo No. 624
EETInfo No. 625
National Semiconductor Corp.
EETInfo No. 626
EETInfo No. 627
Seiko Instruments Inc.
EETInfo No. 628
EETInfo No. 629
EETInfo No. 630
EETInfo No. 631
EETInfo No. 632