AAT3686_08 Datasheet, PDF (11/23 Pages) Advanced Analogic Technologies – USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger

BatteryManager^TM
PRODUCT DATASHEET
AAT3686
USB Port/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 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
(V_UVLO), 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
(V_MIN), 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
(V_MIN). 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 R_SET, R_SETH, and R_SETL resistors. The AAT3686
remains in constant current charge mode until the bat-
tery reaches the voltage regulation point, V_BAT.
Constant Voltage Charging
The system transitions to a constant voltage charging
mode when the battery voltage reaches the output
charge regulation threshold (V_BAT) 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
(V_RCH).
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.
3686.2007.12.1.11
www.analogictech.com
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