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AAT3681A Datasheet(PDF) 9 Page - Advanced Analogic Technologies |
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AAT3681A Datasheet(HTML) 9 Page - Advanced Analogic Technologies |
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9 / 17 page  AAT3681A 500mA USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger 3681A.2007.10.1.2 9 Battery Preconditioning Before the start of charging, the AAT3681A checks several conditions in order to assure a safe charging environment. The input supply must be above the minimum operating voltage, or under-voltage lock- out threshold (V UVLO), for the charging sequence to begin. When these conditions have been met and a battery is connected to the BAT pin, the AAT3681A checks the state of the battery. If the cell voltage is below the preconditioning voltage threshold (V MIN), the charge control begins preconditioning the cell. The battery preconditioning trickle charge current is equal to the fast charge constant current divided by 10. For example, if the programmed fast charge cur- rent is 300mA, then the preconditioning mode (trick- le charge) current will be 30mA. Cell preconditioning is a safety precaution for deeply discharged battery cells and also aids in limiting power dissipation in the pass transistor when the voltage across the device is at the greatest potential. Constant Current Charging Battery cell preconditioning continues until the volt- age on the BAT pin exceeds the preconditioning voltage threshold (V MIN). At this point, the AAT3681A begins the constant current charging phase. The charge constant current (I CH) amplitude is programmed by the user via the R SET resistor. The AAT3681A remains in the constant current charge mode until the battery reaches the voltage regulation point, V BAT_EOC. Constant Voltage Charging The system transitions to a constant voltage charg- ing mode when the battery voltage reaches the output charge regulation threshold (V BAT_EOC) dur- ing the constant current fast charge phase. The regulation voltage level is factory programmed to 4.2V (±0.5%). Charge current in the constant volt- age 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 10% of the pro- grammed fast charge current level in the constant voltage mode, the device terminates charging and goes into a sleep state. The charger will remain in a sleep state until the battery voltage decreases to a level below the battery recharge voltage thresh- old (V RCH). (AAT3681A-3 does not terminate charging and thus does not go into the sleep state. AAT3681A-3 continues to source current to the battery and allows the charge current to asymptot- ically approach zero while in constant voltage charging mode.) Consuming very low current in sleep state, the AAT3681A minimizes battery drain when it is not charging. This feature is particularly useful in appli- cations where the input supply level may fall below the battery charge or under-voltage lockout level. In such cases where the AAT3681A input voltage drops, the device will enter sleep state and auto- matically resume charging once the input supply has recovered from the fault condition. Figure 1: Current vs. Voltage Profile During Charging Phases. Constant Current Charge Phase Constant Voltage Charge Phase Preconditioning Trickle Charge Phase Charge Complete Voltage Constant Current Mode Voltage Threshold Regulated Current Trickle Charge and Termination Threshold I = CC / 10 I = Max CC |
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