AAT3680
Lithium-Ion/Polymer
Linear Battery Charge Controller
Functional Block Diagram
Microcontroller
Read Enable
2x Trickle
Charge
Control
Current Loop
Error Amp
T2X
CSI
Loop Select
MUX Driver
DRV
Microcontroller
Status Generator
STAT
V
REF
Voltage Loop
Error Amp
Charge Status
Logic Control
MUX
BAT
Voltage
Comparator
LED Signal
Generator
TS
Temperature Sense
Comparator
VSS
VP
Power-On
Reset
Under-
Voltage
Lock Out
Over-Current /
Short-Circuit
Protection
Functional Description
The AAT3680 is a linear charge controller designed
for single-cell lithium-ion/polymer batteries. It is a
full-featured battery management system IC with
multiple levels of integrated power savings, system
communication, and protection. Refer to the block
diagram (above) and flow chart (Figure 1) in this
section for details.
Cell Preconditioning
Before the start of charging, the AAT3680 checks
several conditions in order to maintain a safe charg-
ing environment. 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,
must be within the proper window for safe charging.
When these conditions have been met and a bat-
tery is connected to the BAT pin, the AAT3680
checks the state of the battery. If the cell voltage is
below V
MIN
, the AAT3680 begins preconditioning
the cell. This is performed by charging the cell with
10% of the programmed constant current. For
3680.2006.03.1.6
example, if the programmed charge current is
500mA, then the preconditioning mode (trickle
charge) current will be 50mA. Cell preconditioning
is a safety precaution for deeply discharged cells
and, furthermore, limits power dissipation in the
pass transistor when the voltage across the device
is largest. The AAT3680 features an optional T2X
mode, which allows faster trickle charging at
approximately two times the default rate. This
mode is selected by connecting the T2X pin to V
SS
.
If an over-temperature fault is triggered, the fast
trickle charge will be latched off, and the AAT3680
will continue at the default 10% charge current.
Constant Current Charging
Cell preconditioning continues until the voltage on
the BAT pin reaches V
MIN
. At this point, the
AAT3680 begins constant current charging (fast
charging). Current level for this mode is pro-
grammed using a current sense resistor R
SENSE
between the VP and CSI pins. The CSI pin moni-
tors the voltage across R
SENSE
to provide feedback
for the current control loop. The AAT3680 remains
in constant current charge mode until the battery
reaches the voltage regulation point, V
CH
.
5
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
