AAT3680 Datasheet, PDF (5/18 Pages) Advanced Analogic Technologies – Lithium-Ion Linear Battery Charge Controller

AAT3680
Lithium-Ion Linear Battery Charge Controller
Functional Block Diagram
T2X
CSI
BAT
TS
VP
Microcontroller
Read Enable
2x Trickle
Charge
Control
Current Loop
Error Amp
Loop Select
MUX Driver
V_REF
Voltage Loop
Error Amp
Charge Status
Logic Control
Voltage
Comparator
Microcontroller
Status Generator
MUX
LED Signal
Generator
Temperature Sense
Comparator
Power-On
Reset
Under
Voltage
Lock Out
Over Current /
Short Circuit
Protection
DRV
STAT
V_SS
Functional Description
The AAT3680 is a Linear Charge Controller
designed for one and two cell Lithium Ion or
Lithium Polymer batteries. It is a full-featured bat-
tery management system IC with multiple levels of
power savings, system communication and protec-
tion integrated inside. Refer to the block diagram
and flow chart in this section.
Cell Preconditioning
Before starting charging, the AAT3680 checks sev-
eral conditions in order to maintain a safe charging
environment. The input supply must be above the
minimum operating voltage, or undervoltage lock-
out threshold (V_UVLO), for the charging sequence to
begin. Also, the cell temperature, as reported by a
thermistor connected to TS pin, must be within the
proper window for safe charging. When these con-
ditions have been met, and a battery 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 pro-
grammed constant-current amount. For 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
the 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-tempera-
ture 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
The 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 V_P and CSI pins. The CSI pin monitors the
voltage across R_SENSE to provide feedback for the
current control loop. The AAT3680 remains in con-
stant current charge mode until the battery reaches
the voltage regulation point, V_CH.
3680.2003.4.0.91
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