Design of mobile phone battery charger based on MAXl898

Summary:

Precharge

After the battery is installed, the input DC power is turned on, and the timer is reset when the charger detects the battery, thereby entering the pre-charging process, during which the charger charges the battery with 10% of the fast charging current, so that the battery voltage, The temperature returns to normal. The precharge time is determined by the external capacitor CcT (45 minutes at 100nF). If the battery voltage reaches 2.5V during the precharge time and the battery temperature is normal, the charge enters the fast charge process; if the precharge time is exceeded, the battery voltage remains. Below 2.5V, the battery is considered to be unchargeable, the charger indicates a battery failure, and the LED indicator flashes. 2. The fast charge fast charge process is also called constant current charge. At this time, the charger charges the battery with a constant current. When the constant current is charged, the battery voltage rises slowly. Once the battery voltage reaches the set termination voltage, the constant current charge is terminated, the charging current is rapidly decremented, and the charging enters a full charge process. 3. During full charge, the charging current is gradually attenuated until the charging rate drops below the set value, or the full charge time expires, and the top end is turned off. When the top is turned off, the charger replenishes the battery with a very small charging current. Since the charger has a charging current through the internal resistance of the battery when detecting whether the battery voltage reaches the termination voltage, although the charging current gradually decreases during the full charge and the top cut-off charging, the internal resistance of the battery and other series resistances are reduced. The effect, but the voltage drop formed by the resistors connected in series in the charging loop still has an effect on the detection of the battery termination voltage. Under normal circumstances, full charge and top cutoff charge can extend the battery life of 5% to 10%. 4. Power-off When the battery is fully charged, the pulse level sent by the No. 2 pin of the MAXl898 chip will go from low to high. This will be detected by the MCU, causing the interrupt of the MCU. In the interruption, if it is judged that the charging is completed, Then the MCU will control the optocoupler 6N137 through the P2.0 port to cut off the power supply of the LM7805 to the MAXl898, thus ensuring the safety of the chip and the battery, and also reducing the power consumption. 5. Alarm When the battery is fully charged, the MAXl898 chip itself will extinguish the external LED green light. However, for the sake of safety, after detecting the pulse of full state, the MCU will not only automatically cut off the power supply of the MAXl898 chip, but also alarm through the buzzer to remind the user to remove the battery in time. When the charging error occurs, the MAXl898 chip itself controls the LED green light to flash at a frequency of about 1.5 Hz. At this time, do not cut off the power supply of the chip, so that the user always sees this prompt.

Internal circuit of charging chip MAXl898

See the upload document for the minimum system details of the microcontroller.