AAT3681AIJS-4.2-2-T1 ANALOGICTECH [Advanced Analogic Technologies], AAT3681AIJS-4.2-2-T1 Datasheet - Page 12

• Manufacturer Part Number: AAT3681AIJS-4.2-2-T1
• Description: 500mA USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

Protection Circuitry
Over-Voltage Protection
An over-voltage event is defined as a condition
where the voltage on the BAT pin exceeds the
maximum battery charge voltage and is set by the
over-voltage protection threshold (V
voltage condition occurs, the AAT3681A charge
control will shut down the device until voltage on
the BAT pin drops below V
resume normal charging operation after the over-
voltage condition is removed.
Over-Temperature Shutdown
The AAT3681A has a thermal protection control cir-
cuit which will shut down charging functions should
the internal die temperature exceed the preset ther-
mal limit threshold. Once the internal die tempera-
ture falls below the thermal limit, normal operation
will resume the previous charging state.
Charge Status Output
The AAT3681A 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:
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.
1. AAT3681A-3 does not terminate charging. However, the status pin turns off when I
12
V
BAT_EOC
Battery charging via adapter
No battery charging activity
Event Description
Charging completed
Table 2: LED Status Indicator.
- 0.1V.
or USB port
1
OVP
. The AAT3681A will
OVP
Status
). If an over-
OFF
OFF
ON
Lithium-Ion/Polymer Battery Charger
The required ballast resistor values can be esti-
mated using the following formulas:
Example:
Note: Red LED forward voltage (V
2.0V @ 2mA.
Thermal Considerations
The AAT3681A is offered in a SC70JW-8 package
which can provide up to 687mW of power dissipa-
tion when it is properly bonded to a printed circuit
board and has a maximum thermal resistance of
160°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 gen-
erating devices in a given application design. The
ambient temperature around the charger IC will
also have an effect on the thermal limits of a bat-
tery 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
situation should be calculated:
Where:
P
θ
T
T
JA
J(MAX)
A
D(MAX)
500mA USB Port or AC Adapter
= Maximum Power Dissipation (W)
= Package Thermal Resistance (°C/W)
= Maximum Device Junction Temperature
= Ambient Temperature (°C)
(°C) [135°C]
R
1
BAT
P
=
R
D(MAX)
≤ I
1
(5.5V - 2.0 V)
=
TERM
(V
=
2mA
ADP
and turns back on when V
(T
I
- V
J(MAX)
LED
F(LED)
θ
AAT3681A
JA
= 1.75kΩ
- T
)
A
)
3681A.2007.10.1.2
F
) is typically
BAT
≤