AAT3663 Datasheet, PDF (15/22 Pages) Advanced Analogic Technologies – 1A Linear Li-Ion Battery Charger for Single and Dual Cell Applications

AAT3663
1A Linear Li-Ion Battery Charger
for Single and Dual Cell Applications
by just using the STAT1 pin and a single LED.
Using two LEDs and both STAT pins simply gives
the user more information for the various charging
states. Refer to Table 2 for LED display definitions.
The LED anodes should be connected to the
charger power source input (IN pin).
Event Description
Charge enabled without battery
Battery charging
Charging completed
Fault
STAT1
Flash¹
ON
OFF
OFF
STAT2
Flash¹
OFF
ON
OFF
Table 2: LED Status Indicator Truth Table.
Input Power Present Indicator
The ADDP# pin provides an additional open drain
N-channel MOSFET switch to indicate the pres-
ence of power applied to the charger input (IN pin).
This function may either be used to control an addi-
tion 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
necessary to create reasonable illumination; there-
fore, a ballast 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 package, 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 esti-
mated using the following formula:
Example:
R_BALLAST =
(V_IN - V_F(LED))
I_LED
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
control pass device for the adapter mode, a special
thermal loop control system has been employed to
maximize charging current under all operation con-
ditions. The thermal management system meas-
ures the internal circuit 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
temperature every 1.5 seconds and adjusts the fast
charge current back up in small steps to the full fast
charge current level or until an equilibrium current
is discovered and maximized for the given ambient
temperature condition. 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.
1. Flashing rate depends on output capacitance.
3663.2007.10.1.0
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