AAT3681_08 Datasheet, PDF (9/15 Pages) Advanced Analogic Technologies – USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger

BatteryManager^TM
PRODUCT DATASHEET
AAT3681
USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger
Charge Complete Voltage
Regulated Current
Preconditioning
Trickle Charge
Phase
Constant Current
Charge Phase
I = Max CC
Constant Voltage
Charge Phase
Constant Current Mode
Voltage Threshold
Trickle Charge and I = CC / 10
Termination Threshold
Figure 1: Current vs. Voltage Profile During Charging Phases.
Battery Preconditioning
Before the start of charging, the AAT3681 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
(V_UVLO), for the charging sequence to begin. When these
conditions have been met and a battery is connected to
the BAT pin, the AAT3681 checks the state of the bat-
tery. If the cell voltage is below the preconditioning volt-
age threshold (V_MIN), the charge control begins precon-
ditioning the cell. The battery preconditioning trickle
charge current is equal to the fast charge constant cur-
rent divided by 10. For example, if the programmed fast
charge current is 300mA, then the preconditioning mode
(trickle charge) current will be 30mA. Cell precondition-
ing 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 voltage
on the BAT pin exceeds the preconditioning voltage
threshold (V_MIN). At this point, the AAT3681 begins the
constant current charging phase. The charge constant
current (I_CH) amplitude is programmed by the user via
the R_SET resistor. The AAT3681 remains in the constant
current charge mode until the battery reaches the volt-
age regulation point, V_{BAT_EOC}.
Constant Voltage Charging
The system transitions to a constant voltage charging
mode when the battery voltage reaches the output
charge regulation threshold (V_{BAT_EOC}) during the con-
stant current fast charge phase. The regulation voltage
level is factory programmed to 4.2V (±0.5%). Charge
current in the constant voltage mode drops as the bat-
tery 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 volt-
age 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 threshold (V_RCH).
Consuming very low current in sleep state, the AAT3681
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
AAT3681 input voltage drops, the device will enter sleep
state and automatically resume charging once the input
supply has recovered from the fault condition.
3681.2007.12.1.5
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