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Wireless Systems Design

Battery Charger Keeps Circuits From Overheating

Recharging is a necessity for all portable wireless devices. When such devices are recharging, however, they have a tendency to overheat. Linear Technology Corp. wants to address this problem with the introduction of the LTC4059A. This device is a fully integrated linear battery charger in a tiny package. It promises to charge a single-cell Li-Ion battery at 900 mA without overheating itself or the surrounding components.

A patented thermal-regulation scheme prevents the junction temperature of the IC from exceeding 115°C. To achieve this goal, it reduces the charge current during high power or high-ambient-temperature operation. The IC is housed in a very small, 2-×-2-mm DFN package. The complete solution requires only two discrete components (an input capacitor and charge-current program resistor). It fits into a 2.5-×-2.7-mm footprint. Applications for this device include digital still cameras; portable point-of-sale and diagnostic equipment; and cell phones, PDAs, and USB-equipped handheld devices.

The LTC4059A features an open drain status pin. This pin indicates the presence of an input supply, such as a wall adapter. Among its other features are a charge-current monitor output for charge termination; a 4.2-V, 0.6% accurate float voltage; and 5% charge accuracy. The LTC4059A requires no external MOSFET, sense resistor, or blocking diode. The charge current is adjustable with a standard off-the-shelf resistor. The device operates from input supplies ranging from 3.75 to 8 V including USB ports. During shutdown, the supply current is only 10µA. The battery drain current is less than 1µA.

The LTC4059A is rated for operation from −40° to 85°C. Pricing starts at $1.45 each in 1000-piece quantities.

Linear Technology Corp.
1630 McCarthy Blvd., Milpitas, CA 95035-7417; (408) 432-1900,

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