AAT3686
USB Port/AC Adapter
Lithium-Ion/Polymer Battery Charger
controls the system charge level; therefore, the
AAT3686 will always provide the highest level of
constant current in the fast charge mode possible
for any given ambient temperature condition.
Application Information
AC Adapter / USB System Power Charging
Adapter Mode
Adapter Input Charge Inhibit and Resume
The AAT3686 has an under-voltage lockout and
power on reset feature so that the charger will sus-
pend charging and shut down if the input supply to
the adapter pin drops below the UVLO threshold.
When power is re-applied to the adapter pin or the
UVLO condition recovers and ADP > VBAT, the sys-
tem charge control will assess the state of charge
on the battery cell and will automatically resume
charging in the appropriate mode for the condition
of the battery.
In the adapter mode, constant current charge lev-
els up to 1.5A can be programmed by the user. The
AAT3686 system control will always select the
adapter input over the USB supply input whenever
adapter voltage is present on the ADP pin. The
AAT3686 will operate from the adapter input over a
4.0V to 5.5V range.
The constant current fast charge current for the
adapter input mode is set by the RSET resistor con-
nected between the ADPSET and ground. Refer to
Table 1 for recommended RSET values for a desired
constant current charge level. The presence of volt-
age on the adapter input is indicated by the ADPP#
pin function. This indicator pin is an open drain and
will pull the ADPP# pin low when voltage is detect-
ed on the ADP pin. The precise charging function in
the adapter mode may be read from the DATA pin
and/or status LEDs. Please refer to the Battery
Charge Status Indication discussion in this
datasheet for further details on data reporting.
USB Mode
The AAT3686 provides an input for intelligent USB
charging. When no voltage is present on the
adapter input pin, the charge controller will automat-
ically switch to accepting power from the USB input.
The USB charge mode provides two programmable
fast charge levels up to 500mA each, USB high and
USB low, USBH and USBL, respectively. The USBH
or USBL modes may be externally selected by the
USB select pin (USBSEL). USBSEL is internally
pulled low through a 1MΩ resistor. When the USB-
SEL pin is connected to a logic high level, the USBH
level will be active. Conversely, when USBSEL is
pulled to a logic low level (ground), the USBL level
will be used for charging. Typically, USBH is set for
500mA and USBL is set for 100mA. However, these
two USB charge levels may be user programmed to
any level between 50mA and 500mA by selecting
Thermal Loop Control
Due to the integrated nature of the linear charging
control pass device for the adapter mode, a special
thermal loop control system has been employed to
maximize charging current under all operation condi-
tions. The thermal management system measures
the internal circuit die temperature and reduces the
fast charge current when the device exceeds a pre-
set internal temperature control threshold. Once the
thermal loop control becomes active, the fast charge
current is initially reduced by a factor of 0.44.
the appropriate resistor values for RSETH and RSETL
.
Refer to Table 1 for recommended RSETH and RSETL
values for the desired USB input constant current
charge levels.
The initial thermal loop current can be estimated by
the following equation:
USB Charge Reduction
In many instances, product system designers do not
know the real properties of a potential USB port used
to supply power to the battery charger. Typically,
powered USB ports found on desktop and notebook
PCs should supply up to 500mA. In the event a USB
port being used to supply the charger is unable to
provide the programmed fast charge current or if the
system under charge must also share supply current
with other functions, the AAT3686 will automatically
reduce USB fast charge current to maintain port
integrity and protect the host system.
ITLOOP = ICC · 0.44
The thermal loop control re-evaluates the circuit die
temperature every three seconds and adjusts the
fast charge current back up in small steps to the full
fast charge current level or until an equilibrium cur-
rent is discovered and maximized for the given
ambient temperature condition. The thermal loop
3686.2006.10.1.9
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
