AAT3686_08 Datasheet, PDF (13/23 Pages) Advanced Analogic Technologies – USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger

BatteryManager^TM
PRODUCT DATASHEET
AAT3686
USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger
Application Information
AC Adapter / USB System
Power Charging
Adapter Mode
In the adapter mode, constant current charge levels 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 pres-
ent 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 R_SET resistor connected between
the ADPSET and ground. Refer to Table 1 for recom-
mended R_SET values for a desired constant current charge
level. The presence of voltage 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 detected 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.
Thermal Loop Control
Due to the integrated nature of the linear charging con-
trol pass device for the adapter mode, a special thermal
loop control system has been employed to maximize
charging current under all operation conditions. The
thermal management system measures the internal cir-
cuit die temperature and reduces the fast charge current
when the device exceeds a preset 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 initial thermal loop current can be estimated by the
following equation:
I_TLOOP = I_CC · 0.44
The thermal loop control re-evaluates the circuit die tem-
perature every three seconds and adjusts the fast charge
current back up in small steps to the full fast charge cur-
rent level or until an equilibrium current is discovered
and maximized for the given ambient temperature condi-
tion. The thermal loop 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.
Adapter Input Charge Inhibit and Resume
The AAT3686 has an under-voltage lockout and power
on reset feature so that the charger will suspend charg-
ing 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 recov-
ers and ADP > V_BAT, the system charge control will assess
the state of charge on the battery cell and will auto-
matically resume charging in the appropriate mode for
the condition of the battery.
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 automatically 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 exter-
nally selected by the USB select pin (USBSEL). USBSEL
is internally pulled low through a 1MΩ resistor. When
the USBSEL 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 the appropriate
resistor values for R_SETH and R_SETL. Refer to Table 1 for
recommended R_SETH and R_SETL values for the desired USB
input constant current charge levels.
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 pro-
grammed fast charge current or if the system under
charge must also share supply current with other func-
tions, the AAT3686 will automatically reduce USB fast
charge current to maintain port integrity and protect the
host system.
3686.2007.12.1.11
www.analogictech.com
13