AAT3672 Datasheet, PDF (20/27 Pages) Skyworks Solutions Inc. – 1.6A Dynamic Battery Charger and Power Manager

DATA SHEET
AAT3672
1.6A Dynamic Battery Charger and Power Manager
Status Indicator Display
Simple system charging status states can be displayed
using one LED each in conjunction with the STAT1 and
STAT2 pins of the AAT3672-1/-2 and the STAT1 pin of the
AAT3672-3. These pins have simple switches connecting
the LED’s cathodes to ground. Refer to Tables 5, 6, and 7
for LED display definitions. The LED anodes should be
connected to V_ADP, 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 cathode
and the STAT1 and STAT2 pins of the AAT3672-1/-2 and
the STAT1 pin of the AAT3672-3. A 2mA bias current
should be sufficient to drive most low cost green or red
LEDs. It is not recommended to exceed 8mA when driving
an individual status LED.
The required ballast resistor value can be estimated
using the following formulas:
When connecting to the adapter supply with a red LED:
R_B(STAT1,2) =
V_ADP - V_FLED
I_LED(STAT1,2)
Example:
R_B(STAT1,2) =
5.5V - 2.0V
2mA
= 1.75kΩ
Red LED forward voltage (V_F) is typically 2.0V @ 2mA.
When connecting to the USB supply with a green LED:
R_B(STAT1,2) =
V_USB - V_FLED
I_LED(STAT1,2)
Example:
R_B(STAT1,2) =
5.0V - 3.2V
2mA
= 900Ω
Green LED forward voltage (V_F) is typically 3.2V @ 2mA.
Protection Circuitry
Thermal Loop Control
Due to the integrated nature of the linear charging con-
trol pass devices for both the adapter and USB modes, a
special thermal loop control system has been employed
to maximize charging current under all operating condi-
tions.
The thermal management system measures the internal
circuit die temperature and reduces the charge current
when the device exceeds a preset internal temperature
control threshold. Once the thermal loop control becomes
active, the constant charge current is initially reduced by
a factor of 0.44.
The initial thermal loop current can be estimated by the
following equation:
Constant Charging: I_TLOOP = I_CCADP · 0.44
The thermal loop control re-evaluates the internal die
temperature every three seconds and adjusts the fast
charge current back up in small steps up to the full fast
charge current level or until an equilibrium current is
discovered and maximized for the given ambient tem-
perature condition. In this manner, the thermal loop
controls the system charge level. The AAT3672 will
always provide the highest possible level of constant cur-
rent in the fast charge mode for any given ambient tem-
perature condition.
Programmable Watchdog Timer
The AAT3672 contains a watchdog timing circuit which
operates in all charging modes. Typically a 0.1μF ceram-
ic capacitor is connected between the CT pin and ground.
When a 0.1μF ceramic capacitor is used, the device will
time a shutdown condition if the trickle charge mode
exceeds 50 minutes. When the device transitions to the
trickle charge to the fast charge constant current mode
and then to the constant voltage mode, the timing coun-
ter is reset and will time out after 6 hours.
Summary for a 0.1μF used for the timing capacitor:
Trickle Charge (TC) time out = 50 minutes
Fast Charge Constant Current (CC) + Constant Voltage
(VC) mode time out = 6 hours
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 time out time
of the CC + CV modes would be doubled. The corre-
sponding trickle charge time out time would be the com-
bined CC + VC time divided by 8.
If the programmable watchdog timer function is not
needed it may be disabled the terminating the CT pin to
ground. The CT pin should not be left floating or not
terminated; this will cause errors in the internal timing
control circuit.
The charge timer control will suspend the timing count in
any given mode in the event a fault condition occurs.
Such fault conditions include digital thermal loop charge
current reduction, battery charge reduction, battery tem-
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201880B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012