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Compact fuel gauge blends LED drivers, push-button input

Posted: 20 Feb 2008 ?? ?Print Version ?Bookmark and Share

Keywords:Maxim DS2788? multicell fuel gauge? LED drivers pushbutton?

Maxim Integrated Products has introduced the DS2788, which the company claims is the smallest standalone fuel gauge to integrate LED drivers and a push-button input for multiple Li+ cells into a single IC. Designed for the tight space of a battery pack, it available in a lead-free 14-pin TSSOP. The DS2788 is tailored for displaying the remaining battery capacity of power tools, e-bikes, portable household appliances, and ultramobile PCs.

According to Maxim, the DS2788 reports a battery pack's remaining capacity in both "mAh remaining" and "percentage of full" to the host system, and displays the results using either four or all five of its integrated LED driver outputs. Capable of directly sinking current, each LED driver pin requires only a single resistor to set its current in the LED display, says Maxim, reducing board space and system cost. A programmable I/O pin that can be configured as a debounced-push-button input enables the LED display.

Meanwhile, to reduce the need for software development and shorten time-to-market, the DS2788 utilizes an embedded fuel gauge algorithm to calculate remaining capacity based on precision coulomb count, discharge rate, temperature, and cell characteristics, along with precision battery-current and voltage measurements. The fuel gauge monitors battery packs with multiple Li+ cells by allowing internal gain calibration of an external voltage-divider that feeds the battery-voltage-measurement input. To conserve battery power, a pin for driving external FET switches enables the voltage-divider only during voltage measurement. An estimate of the battery pack's capacity is communicated to the host over a 1-Wire interface, which reduces the number of necessary contacts between the pack and the host to as few as three.

Additionally, the DS2788 features 16bytes of EEPROM that can be used to facilitate battery lot and date tracking, as well as for the non-volatile storage of system or battery-usage statistics. A unique, factory-programmed 64bit ROM ID assures that no two DS2788s are alike and enables absolute battery-pack traceability.

Price starts at $2.72 for 1,000 units and above.




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