AAT3698 Datasheet, PDF (16/21 Pages) Skyworks Solutions Inc. – 1.6A Linear Li-Ion Battery Charger in a 3x3 TDFN Package

DATA SHEET
AAT3698
1.6A Linear Li-Ion Battery Charger in a 3x3 TDFN Package
Use the following formula to set the charge termination
current, I_{CH_TERM}.
I_{CH_TERM} =
15μA · R_TERM
2V
· I_{CH_CC}
I_{CH_TERM} is set by default to 10% of I_{CH_CC} when the TERM
pin is connected to the INCHR pin.
When the charge current reaches the termination current,
the STAT pin will be set to high impedance, but the charge
termination current will continue to flow until the EN pin
is toggled high. To set charge termination current thresh-
old to the lowest level, connect the TERM pin to ground.
Battery Connection
A single cell Li-Ion/Polymer battery should be connected
between the BAT pin and ground.
Status Indicator Display
Simple system charging status can be displayed using a
single LED in conjunction with the AAT3698-1/-2's STAT
pin. This pin has a simple switch connecting the LED’s
cathode to ground. Refer to Table 1 for LED display
definitions. The LED anodes should be connected to
INCHR or other system power supply that does not
exceed 7V, depending upon system design require-
ments. The LED should be biased with as little current as
necessary to create reasonable illumination; therefore, a
ballast resistor should be placed between the LED cath-
ode and the STAT pin. LED current consumption will add
to the overall thermal power budget for the device pack-
age, so it is wise to keep the LED drive current to a
minimum. 2mA should be sufficient to drive most low-
cost green or red LEDs. Driving an individual status LED
with over 8mA is not recommended.
The required ballast resistor value can be estimated
using the following formulas:
When connecting to the adapter supply with a red LED:
R_B(STAT) =
V_ADP - V_F(LED)
I_LED(STAT)
Example:
5.5V - 2.0V
R_B(STAT) =
2mA
= 1.75kΩ
Note: Red LED forward voltage (V_F) is typically 2.0V @
2mA.
When connecting to the USB supply with a green LED:
Example:
R_B(STAT) =
V_USB - V_F(LED)
I_LED(STAT)
5.0V - 3.2V
R_B(STAT) =
2mA
= 900Ω
Note: Green LED forward voltage (V_F) is typically 3.2V @
2mA.
Capacitor Selection
Input Capacitor (IN)
A 1μF or larger capacitor is typically recommended for
C_IN. C_IN should be located as close to the device IN pin
as practically possible. Ceramic, tantalum, or aluminum
electrolytic capacitors may be selected for C_IN. There is
no specific capacitor equivalent series resistance (ESR)
requirement for C_IN. However, for higher current opera-
tion, ceramic capacitors are recommended for C_IN due to
their inherent capability over tantalum capacitors to
withstand input current surges from low impedance
sources such as batteries in portable devices.
Typically, 50V rated capacitors are required for the appli-
cation to prevent any surge voltage. Ceramic capacitors
selected as small as 1206 are available which can meet
these requirements. Capacitors with other voltage rating
can also be used for known input voltage applications.
Charger Input Capacitor (INCHR)
A 1μF decoupling capacitor is recommended to be placed
between INCHR and GND. This capacitor should be locat-
ed as closely and routed as directly as practically possible
to the device's INCHR pin with a good ground return path
for maximum device over-voltage protection perfor-
mance.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201902B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 27, 2012