Power Electronics

Smart ICs Efficiently Charge Li-Ion and Polymer Batteries

As notebooks, PDAs, smart phones and other battery-powered mobile products proliferate, battery-power management continues to garner special attention. Semiconductor suppliers continue to launch battery management devices aimed at improving charging schemes, battery life, and reliability. With all this industry growth, suppliers such as Advanced Analogic Technologies, Intersil, and Texas Instruments (TI) have recently launched ICs to improve power solutions for mobile products driven by Li-ion and Li-polymer batteries.

While Advanced Analogic Technologies' newest linear battery charge controller, the AAT3680, has been designed to support either a one- or a two-cell (4.2V or 8.4V) Li-ion or Li-poly pack, Intersil's AnyAdapter charger IC is aimed at a wide variety of portable devices. And Texas Instruments has unwrapped a highly integrated power chip that is tailored for single cell Li-ion or Li-poly powered applications that contain multiple power rails.

Advanced Analogic Technologies' AAT3680 is crafted to handle all charging modes, including trickle charge, constant current, and constant voltage. The unit provides a complete set of protection features for overcurrent, overvoltage, and temperature protection.

Like all Li-ion chargers, the AAT3680 provides a status output to support an LED indicator light for the charging process. To inform the system of the state of the battery, it also provides a 1 MHz microprocessor serial interface and accepts an input voltage of 4.5V to 15V.

Built with an array of protection circuits, the charger monitors conditions. In the event of a failure, it automatically shuts down to protect the charger and battery under charge. The AAT-3680 is designed to operate with a low-cost pnp transistor or P-channel power MOSFET. It's housed in an 8-pin miniature small-outline package (MSOP) or in a compact 12-pin TSOPJW (J-lead wide body).

Near Chip-Scale Package

Encased in a near-chip-scale 3 mm × 3 mm dual flat no-lead (DFN) package, Intersil's AnyAdapter ISL6292 accepts a wide range of voltage sources, including voltage and current limited wall-plug modules and USB bus power (see the figure). Besides saving valuable board space, this next-generation Li-ion/Li-poly charger offers high thermal efficiency along with full voltage protection, current protection and the company's proprietary Thermaguard temperature-controlled charge-rate protection.

The ISL6292 operates as a linear charger when the ac adapter is a voltage source by charging the cell in a constant-current (CC) then constant-voltage (CV) profile. Charge current is resistor programmable up to a maximum of 2A. It also combines the benefits of a linear and pulse charger. According to the maker, AnyAdapter technology cuts thermal dissipation drastically to enable a significant reduction in charge time for similar operating conditions.

An internal trimmed current-sense circuit guarantees 10% accuracy with no bulky external current-sense resistor. The constant voltage is either 4.1V (ISL6292-1CRX) or 4.2V (ISL6292-2CRX) with 1% accuracy. The ISL6292 always preconditions the battery with one-tenth of the programmed charge current at the beginning of a charge cycle until it verifies that the battery can be fast-charged.

Using Thermaguard protection to ensure safe operation, it reduces design complexity and avoids premature charge termination invoked by the thermal shutdown feature of older-generation solutions, according to Dean F. Henderson, Intersil's director for portable products. If conditions cause the ISL6292 die temperature to approach a set limit, the internal temperature control activates, reducing the charge current (folding it back) to maintain a safe temperature. As the cell voltage increases with charge, the thermal control permits charge current to increase to shorten the charge cycle. It automatically recharges the battery when the cell voltage drops below a recharge threshold.

Package options for the ISL6292-1CR and ISL6292-2CR include the 10-pad 3 mm × 3 mm DFN, the 16-pad 4 mm × 4 mm QFN and the 16-pad 5 mm × 5 mm QFN. All of these packages are thermally enhanced, offering low thermal resistance for heat transfer to the board.

Integrated Charger

Exploiting advanced 0.65 micron biCMOS process with lateral DMOS, TI has readied a smart battery power management chip that integrates on a single die high performance battery charging functions with dc-dc conversion circuitry. Developed for a single cell Li-ion or Li-poly battery powered mobile products, a single TPS65010 can address multiple voltage needs of today's smart phones, PDAs, and other mobile applications, noted Dave Heacock, director of TI's portable power management business.

Encased in a 48-lead 7 mm × 7 mm QFN package, the TPS65010 integrates two synchronous step-down dc-dc converters with 1A USB/ac charger and two 200mA low dropout (LDO) regulators. It also incorporates I2C interface, dual input ports for charging from USB or wall plug, four general purpose I/Os, and control signals. The built-in linear charger selects the USB port or ac adapter as the charging source for the system. It provides high accuracy current and voltage regulation with charge status indication and termination. An integrated current sensor with programmable current set-point provides design flexibility and cuts the need for external sense resistors. It deploys pulse-frequency and pulse-width modulation switching and offers low quiescent current of 70µA and low-power modes.

The step-down converters include one 400mA converter for processor cores, and a 1A dc-dc for system voltages. Operating with an input voltage range of 1.8V to 6.5V, the LDOs provide additional regulation. Supporting 100 kHz to 400 kHz operation, the I2C compatible interface allows easy control of various operational modes of charging, dc-dc conversion and LDO regulation parameters.

Advanced Analogic Technologies, Sunnyvale, Calif., www.analogictech.com
CIRCLE 346 on Reader Service Card

Intersil Corp., Palm Bay, Fla., www.intersil.com
CIRCLE 347 on Reader Service Card

Texas Instruments Inc., Dallas, www.ti.com
CIRCLE 348 on Reader Service Card

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