The XB5352 monitors the voltage and current of a battery and protects it from being damaged due to overcharge voltage, overdischarge voltage, overdischarge current, and short circuit conditions by disconnecting the battery from the load or charger. These functions are required in order to operate the battery cell within specified limits. The device requires only one external capacitor. The MOSFET is integrated and its RSS(ON) is as low as 45mΩ typical. Normal operating mode If no exception condition is detected, charging and discharging can be carried out freely. This condition is called the normal operating mode. Overcharge Condition When the battery voltage becomes higher than the overcharge detection voltage (VCU) during charging under normal conditionand the state continues for the overcharge detection delay time (tCU) or longer, the XB5352 turns the charging control FET off to stop charging. This condition is called the overcharge condition. The overcharge condition is released in the following two cases: 1, When the battery voltage drops below the overcharge release voltage (VCL), the XB5352 turns the charging control FET on and returns to the normal condition. 2, When a load is connected and discharging starts, the XB5352 turns the charging control FET on and returns to the normal condition. The release mechanism is as follows: the discharging current flows through an internal parasitic diode of the charging FET immediately after a load is connected and discharging starts, and the VM pin voltage increases about 0.7 V (forward voltage of the diode) from the GND pin voltage momentarily. The XB5352 detects this voltage and releases the overcharge condition. Consequently, in the case that the battery voltage is equal to or lower than the overcharge detection voltage (VCU), the XB5352returns to the normal condition immediately, but in the case the battery voltage is higher than the overcharge detection voltage (VCU),the chip does not return to the normal condition until the battery voltage drops below the overcharge detection voltage (VCU) even if the load is connected. In addition, if the VM pin voltage is equal to or lower than the overcurrent 1 detection voltage when a load is connected and discharging starts, the chip does not return to the normal condition. Remark If the battery is charged to a voltage higher than the overcharge detection voltage (VCU) and the battery voltage does not drops below the overcharge detection voltage (VCU) even when a heavy load, which causes an overcurrent, is connected, the overcurrent 1 and overcurrent 2 do not work until the battery voltage drops below the overcharge detection voltage (VCU). Since an actual battery has, however, an internal impedance of several dozens of mΩ , and the battery voltage drops immediately after a heavy load which causes an overcurrent is connected, the overcurrent 1 and overcurrent 2 work. Detection of load short-circuiting works regardless of the battery voltage.
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