AAT3672 Datasheet, PDF (13/27 Pages) Skyworks Solutions Inc. – 1.6A Dynamic Battery Charger and Power Manager

DATA SHEET
AAT3672
1.6A Dynamic Battery Charger and Power Manager
case of USB charging from a USB port V_USB supply, there
are two events which need to be guarded against. The
first is charging from a defective or inadequate USB host
supply; the second problem could arise if the programmed
charge current plus the system supply demand through
the AAT3672 exceeds the ability of a given USB port. In
either case, the AAT3672 charge reduction (CHR) loop will
activate when the input source drops below the V_{CHR_TH}
threshold of 4.5V. The CHR loop will automatically reduce
the charge current to the battery until the supply voltage
recovers to a point above the V_{CHR_TH} threshold. This
unique feature protects the charger, system and source
supply in the event an adapter or power source does not
meet the programmed ADP charging mode current
demand. The resulting CHR system will permit the charg-
ing of a battery cell with the maximum possible amount
of charge current for any given source fault condition.
During battery charging, the device temperature can
rise due to power dissipation within the charge current
control device and the load switches. In some cases, the
power dissipation in the device may cause the junction
temperature to rise up to its thermal shutdown thresh-
old. In the event of an internal over-temperature condi-
tion caused by excessive ambient operating temperature
or an excessive power dissipation condition, the AAT3672
utilizes a digitally controlled thermal loop system that
will reduce the charging current to prevent the device
from thermal shutdown. The digital thermal loop will
maintain the maximum possible battery charging cur-
rent for the given set of input to output power dissipa-
tion and ambient temperature conditions.
The digital thermal loop control is dynamic in the sense
that it will continue to adjust the battery charging cur-
rent as operating conditions change. The digital thermal
loop will reset and resume normal operation when the
power dissipation or over temperature conditions are
removed.
Battery temperature and charge state are fully monitored
for fault conditions. In the event of an over voltage, over-
current, or over-temperature failure, the device will auto-
matically shut down, thus protecting the charging device,
control system, and the battery under charge. In addition
to internal charge controller thermal protection, the
AAT3672 also provides a temperature sense feedback
function (TS pin) from the battery to shut down the
device in the event the battery exceeds its own thermal
limit during charging. All fault events are reported to the
user by the simple status LED(s) which is (are) internally
controlled by open drain NMOS switch(es).
Charging Operation
The AAT3672 has four basic modes for the battery
charge cycle: pre-conditioning/trickle charge, constant
current fast charge, constant voltage, and end of charge/
sleep state.
Battery Preconditioning
Before the start of charging, the AAT3672 checks several
conditions in order to assure a safe charging environ-
ment. The input supply must be above the minimum
operating voltage, or under-voltage lockout threshold
(V_UVLO), for the charging sequence to begin. Also, the cell
temperature, as reported by a thermistor connected to
the TS pin from the battery, must be within the proper
window for safe charging. When these conditions have
been met and a battery is connected to the BAT pin, the
AAT3672 checks the state of the battery by sensing the
cell voltage. If the cell voltage is below the precondition-
ing voltage threshold (V_MIN), the AAT3672 begins precon-
ditioning the battery cell.
Fast Charge/Constant Current Charging
Battery cell preconditioning continues until the voltage
measured by the internal sense circuit exceeds the pre-
conditioning voltage threshold (V_MIN). At this point, the
AAT3672 begins the fast charge constant current phase.
The fast charge constant current (I_{CH_CC}) level is pro-
grammed by the user via the R_SET resistor. The AAT3672
remains in constant current charge mode until the bat-
tery reaches the voltage regulation point, V_CO(REG). The
formula for fast charge current as a function of current
setting resistor is:
2V
I_{CH_CC} = K_{I_CC_ADP} · _RSET
Alternately, to select the resistor value for a given charg-
ing current use:
2V
R_SET = K_{I_CC_ADP} · _{ICH_CC}
where K_{I_CC_ADP} = 29300 (typical).
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201880B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012
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