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AAT3686-1 Datasheet(PDF) 11 Page - Advanced Analogic Technologies |
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AAT3686-1 Datasheet(HTML) 11 Page - Advanced Analogic Technologies |
11 / 23 page AAT3686 USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger BatteryManager TM PRODUCT DATASHEET 3686.2007.12.1.11 11 www .analogictech.com Battery Preconditioning Before the start of charging, the AAT3686 checks sev- eral conditions in order to assure a safe charging envi- ronment. The input supply must be above the minimum operating voltage, or under-voltage lockout threshold (VUVLO), for the charging sequence to begin. Also, the cell temperature, as reported by a thermistor connected to the TS pin from the battery, must be within the proper window for safe charging. When these conditions have been met and a battery is connected to the BAT pin, the AAT3686 checks the state of the battery. If the cell volt- age is below the preconditioning voltage threshold (VMIN), the AAT3686 begins preconditioning the cell. The battery preconditioning trickle charge current is equal to the fast charge constant current divided by 10 (USBL divided by 2). For example, if the programmed fast charge current is 500mA, then the preconditioning mode (trickle charge) current will be 50mA. Cell precon- ditioning is a safety precaution for a deeply discharged battery and also aids in limiting power dissipation in the pass transistor when the voltage across the device is at the greatest potential. Fast Charge / Constant Current Charging Cell preconditioning continues until the voltage on the BAT pin exceeds the preconditioning voltage threshold (VMIN). At this point, the AAT3686 begins the constant current fast charging phase. The fast charge constant current (ICC) amplitude is determined by the charge mode, ADP, USBH or USBL, and is programmed by the user via the RSET, RSETH, and RSETL resistors. The AAT3686 remains in constant current charge mode until the bat- tery reaches the voltage regulation point, VBAT. Constant Voltage Charging The system transitions to a constant voltage charging mode when the battery voltage reaches the output charge regulation threshold (VBAT) during the constant current fast charge phase. The regulation voltage level is factory programmed to 4.2V (±1%). Charge current in the constant voltage mode drops as the battery cell under charge reaches its maximum capacity. End of Charge Cycle Termination and Recharge Sequence When the charge current drops to 7.5% (35% for USBL) of the programmed fast charge current level in the con- stant voltage mode, the device terminates charging and goes into a standby state. The charger will remain in a standby state until the battery voltage decreases to a level below the battery recharge voltage threshold (VRCH). When the input supply is disconnected or drops below UVLO or EN = 0, the charger will automatically enter power-saving sleep mode. Consuming an ultra-low 0.3µA in sleep mode (1µA for AAT3686-1), the AAT3686 minimizes battery drain when it is not charging. This feature is particularly useful in applications where the input supply level may fall below the battery charge or under-voltage lockout level. In such cases where the AAT3686 input voltage drops, the device will enter sleep mode and automatically resume charging once the input supply has recovered from its fault condition. Preconditioning Trickle Charge Phase Constant Current Charge Phase Constant Voltage Charge Phase Charge Complete Voltage Constant Current Mode Voltage Threshold Regulated Current Trickle Charge and Termination Threshold I = CC / 10 I = Max CC Figure 1: Current vs. Voltage Profile During Charging Phases. |
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