MIC79110 Simple 1.2A Linear Li-Ion Battery Charger - Micrel - #9

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Micrel, Inc. MIC79110 October 2007 9 M9999-102507 All lithium-ion batteries take approximately 3 hours to charge with the second stage taking twice as long as the first stage. Some chargers claim to be fast chargers by skipping the second stage and just charges the battery until the cell voltage is reached. This only charges the battery to 70% capacity. An increase in the charge current during stage 1 does not shorten the total charge time. It will only shorten the time for stage 1 to complete and lengthen the time in stage 2. The lithium-ion loses charge due to aging whether it is used or not. Do not store the batteries at full charge and high heat because it will accelerate the aging process. Try and store with 40% charge and in a cool environment. Lithium-Ion Safety Precautions Every lithium-ion battery pack should have a safety circuit which monitors the charge and discharge of the pack and prevents dangerous occurrences. The specifications of these safety circuits are dictated by the cell manufacturer and may include the following: • Reverse polarity protection • Charge temperature must not be charged when temperature is lower than 0°C or above 45°C. • Charge current must not be too high, typically below 0.7°C • Discharge current protection to prevent damage due to short circuits. • Protection circuitry for over voltage applied to the battery terminals. • Overcharge protection circuitry to stop charge when the voltage per cell rises above 4.3V. • Over discharge protection circuitry to stop discharge when the battery voltage falls below 2.3V (varies with manufacturer). • Thermal shutdown protection for the battery if the ambient temperature is above 100°C.