Electronic Design

Multiple-Battery Charger IC Tackles Larger Portable Products

Larger portables need lots of power, and Maxim's MAX8730 is up to the job. This precision constant-current,-constant-voltage charger IC charges three or four lithium-ion cells in series at charge currents greater than 3.5 A. It also can charge nickel-metal-hydride and nickel-cadmium cells.

The device can be hardwired or controlled by a microprocessor to set the charging current or voltage. Battery-voltage regulation is accurate to 0.5%, which increases battery capacity and minimizes charging time. A hysteretic comparator detects the presence of an ac power adapter and automatically selects the appropriate power source.

The charge current and input current-sense amplifiers have low-input offset errors, allowing the use of small-value sense resistors. For light loads, the MAX8730 operates in discontinuous conduction mode for improved efficiency. At higher charging currents, this switches to continuous-conduction mode, with inductor current never crossing zero. Analog inputs control input current limit, charge current, and voltage.

The MAX8730's dc-dc converter drives a p-channel MOSFET and uses an external freewheeling Schottky diode. A fold-back feature reduces the Schottky requirement at low battery voltages. An integrated 3.3-V low-dropout can supply over 20 mA to external circuitry or ICs, such as a keyboard controller.

Packaged in a 5- by 5-mm, 28-pin QFN, the MAX8730 costs $5.04 in 1000-unit quantities.

Maxim Integrated Products
www.maxim-ic.com

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