AAT3663_08 Datasheet, PDF (17/23 Pages) Advanced Analogic Technologies – 1A Linear Li-Ion Battery Charger for Single and Dual Cell Applications

BatteryManager^TM
PRODUCT DATASHEET
AAT3663
1A Linear Li-Ion Battery Charger for Single and Dual Cell Applications
The LED anodes should be connected to the charger
power source input (IN pin).
Input Power Present Indicator
The ADDP# pin provides an additional open drain
N-channel MOSFET switch to indicate the presence of
power applied to the charger input (IN pin). This func-
tion may either be used to control an addition status LED
to give a visual indication when input power is applied.
This open drain output may also be pulled high via a pull
up resistor to provide an active low signal to a system
microcontroller to indicate the presence of applied input
power.
Status Display LED Biasing
The LED should be biased with as little current as neces-
sary to create reasonable illumination; therefore, a bal-
last resistor should be placed between the LED cathode
and the STAT pin. LED current consumption will add to
the overall thermal power budget for the device pack-
age, hence it is good to keep the LED drive current to a
minimum. 2mA should be sufficient to drive most low-
cost green or red LEDs. It is not recommended to exceed
8mA for driving an individual status LED.
The required ballast resistor values can be estimated
using the following formula:
R_BALLAST =
(V_IN - V_F(LED))
I_LED
Example:
R_BALLAST =
(5.0V - 2.0V)
2mA
= 1.5kΩ
Note: Red LED forward voltage (V_F) is typically 2.0V @
2mA.
Digital Thermal Loop Control
Due to the integrated nature of the linear charging con-
trol pass device for the adapter mode, a special thermal
loop control system has been employed to maximize
charging current under all operation conditions. The
thermal management system measures the internal cir-
cuit die temperature and reduces the fast charge current
when the device exceeds a preset internal temperature
control threshold. Once the thermal loop control becomes
active, the fast charge current is initially reduced by a
factor of 0.28. The initial thermal loop current can be
estimated by the following equation:
I_TLOOP = I_{CH_CC} · 0.28
The thermal loop control re-evaluates the circuit die tem-
perature every 1.5 seconds and adjusts the fast charge
current back up in small steps to the full fast charge cur-
rent level or until an equilibrium current is discovered
and maximized for the given ambient temperature condi-
tion. The thermal loop controls the system charge level;
therefore, the AAT3663 will always provide the highest
level of constant current in the fast charge mode possible
for any given ambient temperature condition.
Protection Circuitry
Programmable Timer Function
The AAT3663 contains a watchdog timing circuit to shut
down charging functions in the event of a defective bat-
tery cell not accepting a charge over a preset period of
time. Typically, a 0.1μF ceramic capacitor is connected
between the CT pin and ground. When a 0.1μF ceramic
capacitor is used, the device will time out a shutdown
condition if the trickle charge mode exceeds 25 minutes
and a combined trickle charge plus constant current
mode of 3 hours. When the device transitions to the
constant voltage mode, the timing counter is reset and
will time out after an additional 3 hours if the charge
current does not drop to the charge termination level.
The AAT3663 has a battery fault detector, which, when
used in conjunction with a 0.1μF capacitor on the CT pin,
outputs a 1Hz signal with 50% duty cycle at the STAT1
pin in the event of a timeout while in the trickle charge
mode.
Mode
Trickle Charge (TC) Time Out
Trickle Charge (TC) + Constant Current (CC)
Mode Time Out
Constant Voltage (CV) Mode Time Out
Time
25 minutes
3 hours
3 hours
Table 3: Summary for a 0.1μF Ceramic Capacitor
Used for the Timing Capacitor.
The CT pin is driven by a constant current source and
will provide a linear response to increases in the timing
capacitor value. Thus, if the timing capacitor were to be
doubled from the nominal 0.1μF value, the timeout peri-
ods would be doubled. If the programmable watchdog
3663.2008.01.1.2
www.analogictech.com
17