AAT3684 Datasheet, PDF (12/17 Pages) Advanced Analogic Technologies – 500mA USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger

BatteryManager^TM
PRODUCT DATASHEET
AAT3684
500mA USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger
Over-Temperature Shutdown
The AAT3684 has a thermal protection control circuit
which will shut down charging functions should the inter-
nal die temperature exceed the preset thermal limit
threshold. Once the internal die temperature falls below
the thermal limit, the normal operation will resume the
previous charging state.
Charge Status Output
The AAT3684 provides battery charge status via a status
pin. This pin is internally connected to an N-channel open
drain MOSFET, which can be used to drive an external
LED. The status pin can indicate the following conditions:
Event Description
No battery charging activity
Battery charging via adapter or USB port
Charging completed
Status
OFF
ON
OFF
Table 2: LED Status Indicator.
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 formulas:
Example:
R₁=
(V_ADP - V_F(LED))
I_LED
R₁ =
(5.5V - 2.0V)
2mA
= 1.75kΩ
Note: Red LED forward voltage (V_F) is typically 2.0V @
2mA.
Thermal Considerations
The AAT3684 is offered in the STDFN2.2x2.2-10 pack-
age, which can provide up to 2W of power dissipation
when it is properly bonded to a printed circuit board and
has a maximum thermal resistance of 50°C/W. Many
considerations should be taken into account when
designing the printed circuit board layout, as well as the
placement of the charger IC package in proximity to
other heat generating devices in a given application
design. The ambient temperature around the charger IC
will also have an effect on the thermal limits of a battery
charging application. The maximum limits that can be
expected for a given ambient condition can be estimated
by the following discussion.
First, the maximum power dissipation for a given situa-
tion should be calculated:
P_D(MAX) =
(T_J(MAX) - T_A)
θ_JA
Where:
P_D(MAX) = Maximum Power Dissipation (W)
θ_JA = Package Thermal Resistance (°C/W)
T_J(MAX) = Maximum Device Junction Temperature (°C)
[135°C]
T_A = Ambient Temperature (°C)
Figure 3 shows the relationship of maximum power dis-
sipation and ambient temperature of AAT3684.
3.00
2.50
2.00
1.50
1.00
0.50
0.00
0
20
40
60
80
100
T_A (°C)
Figure 3: Maximum Power Dissipation.
12
www.analogictech.com
3684.2007.12.1.2