Fuel gauge extends battery life with suspend mode - Embedded.com

Fuel gauge extends battery life with suspend mode

The DS2756 is a high-precision battery fuel gauge that integrates precise current, voltage, and temperature measurements along with nonvolatile data storage into one IC. Developed by Dallas Semiconductor, the device contains three power states, including active, sleep, and a unique suspend mode. Suspend mode lets the DS2756 optimize its own current drain while other devices in the host enter low-power inactive states. Suspend mode thus extends the battery and operational life of the host product.

Using suspend mode, the DS2756 remains in an ultra-low power state while the host product is in a low-power operative state, such as standby. The IC periodically cycles between suspend mode and active mode to measure current at a reduced supply as low as 10 μA. Cycling between these power states lets the part detect if the pack is being discharged or charged above programmable low-current suspend thresholds. If it detects either of these conditions, it sends a microcontroller or other pack circuitry a wake-up alert to begin normal active operation.

The DS2756 measures current, average current, and accumulated current. Using a 20-mW sense resistor, current accumulation is performed over a range of ±3.2A. An external filtering capacitor allows peak currents of higher values to be integrated in the current-accumulation (fuel-gauging) measurement.

Voltage is measured over a 0- to 4.75-V range with a resolution of 4.88 mV. Temperature is measured over the entire operating range with a resolution of 0.125°C. If either the accumulated current or the temperature measurement exceeds user-programmed limits, the DS2756 sends an interrupt. A snapshot mode lets both current and voltage measurements be synchronized, so the DS2756 can obtain an instantaneous power measurement for a specific single event. All measured data is stored in on-chip EEPROM or SRAM memory, and can reported to the host.

The DS2756 is available in a tiny 8-pin TSSOP package, small enough to fit on the side of a Li+ prismatic cell. Prices start at $1.90 for lots of 1000. A data sheet is available at www.maxim-ic.com/DS2756.

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