Electronic Design

Full-Featured Battery-Charger ICs And Fuel-Gauge IC Take Charge

It's all about power nowadays as consumers snap up portable devices that require more and more juice. Designers are hard pressed to keep users' tanks topped up and to give those users an idea of how far they can go on what's left in those tanks. Maxim's latest solutions include a pair of power-management ICs as well as a programmable fuel gauge that can be built into battery packs.

The MAX8662 and MAX8663 do more than integrate two synchronous buck regulators, a boost regulator driving two to seven white LEDs, four low-dropout linear regulators (LDOs), and a linear charge for a single-cell lithium-ion (Li+) battery (Fig. 1). When system load peaks exceed the external source's capability, both ICs tell the battery to supply whatever supplemental current is needed.

When system load requirements are low, residual power from the external power source will be directed to charging the battery. When external power is connected, the system can operate with no battery or a discharged battery. The external power source can be an ac adapter, an auto adapter, or a USB source. The ICs are intended for smart cellular phones, PDAs, Internet appliances, and other portable devices.

The MAX8663 integrates two high-efficiency step-down dc-dc converters, four LDOs, and the smart charger. The MAX8662 adds the step-up dc-dc converter for up to seven white or organic LED or displays. Specs for both buck converters include up to 97% efficiency at 1- to 3.3-V output. One handles 1.2-A loads, the other 900-mA loads. The four LDOs support 500-, 300-, and two 150-mA loads. Input range is from 1.7 to 5.5 V. The LDOs also have selectable output voltages to eliminate external resistor-dividers and minimize board space.

The charger's dc-input current limit is adjustable up to 2 A. Charge current is adjustable up to 1.5 A to accommodate a wide range of battery capacities. The chips provide thermal regulation, overvoltage protection, charge status and fault outputs, a power-OK monitor, a battery-thermistor monitor, and a charge timer. Pricing starts at $3.95.

The DS2792 from Maxim's Dallas Semiconductor division offers a programmable fuel gauge that can be built into one- or two-cell battery packs. Battery-pack designers who aren't satisfied with pre-programmed fuel-gauging algorithms can use the chip to write their own code or tweak existing code.

The chip integrates a microcontroller, password-protected program memory, data memory, and an accurate measurement system for battery current, voltage, and temperature (Fig. 2). Its computing core is the low-power, 16-bit MAXQ20 microcontroller. Fetch and execution operations are completed in one cycle without pipelining.

A 16-level hardware stack enables fast subroutine calls and task-switching. The DS2792 contains separate program memory, data EEPROM, and data RAM. I/O is via JTAG or a 19.2-kbit/s UART interface. Programming can take place through either port.

Current measurements are internally summed to calculate the accumulated current. That measurement is accurate to within 0.5%, ±4.0 µV, over a range of ±64 mV. Based on the use of a 15-mΩ sense resistor, this translates to 0.5%, ±267 µA, over a 4.2-A range.

The DS2792 measures voltage as a 10-bit value over a 0- to 4.99-V range with a resolution of 4.88 mV. Its temperature sensor measures the temperature of the battery and reports the results as a 10-bit value with a resolution of 0.125°C. Pricing starts at $3.28.

Maxim Integrated Products

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