DALLAS Semiconductor, represented in Australia by Arrow Electronics , has released the DS2715, a versatile NiMH battery-pack charge controller. It can be optimised for a variety of charging scenarios for either removable or embedded battery packs containing one to ten NiMH cells in series.
The charger can be configured as a switched dc charger, a linear current regulator or a switch-mode current source. Charge rates in any configuration can be user-selected with an external sense resistor which enables rates between 0.15°C and a fast 2°C.
The DS2715 implements various charge states to ensure safe and reliable charging. Throughout the entire charge cycle, cell voltage and pack temperature are continuously monitored. The charge cycle begins with a precharge qualification to prevent either fast charging of deeply depleted cells or charging under extreme temperature conditions.
Precharge is performed at a reduced rate until all cells are safe for fast charge. When the cells are ready, fast charging begins and proceeds as long as temperature and cell voltage remain within specified ranges.
The DS2715 terminates charge using an external thermistor to detect the cells' temperature change over time, the dT/dt technique. For added safety, a secondary charge timer backs up the dT/dt termination method. The duration for timing a charge termination is user-selectable with an external resistor from 30 minutes up to six hours. After fast-charge termination, the DS2715 enters top-off for a period equal to half the fast-charge safety-timer setting. A final done stage follows where the DS2715 remains until the cell pack is removed from the charger. All stages of the charge cycle can be displayed to an end-user through the DS2715's two LED outputs. At any time during the charge cycle, the DS2715 switches to a discharge mode when a load is attached to the cell pack.
Typical applications include portable DVD players, portable television sets, handheld gaming, handheld POS terminals and test equipment. The device is available in a 16-pin lead-free SOIC package.