AAT3685 Datasheet, PDF (14/23 Pages) Advanced Analogic Technologies – Lithium-Ion/Polymer Battery Charger

AAT3685
Lithium-Ion/Polymer Battery Charger
Input Charge Inhibit and Resume
The AAT3685 UVLO and power on reset feature
will function when the input pin voltage level drops
below the UVLO threshold. At this point, the charg-
er will suspend charging and shut down. When
power is re-applied to the ADP/USB pin or the
UVLO condition recovers, the system charge con-
trol 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.
Single Path Charging from a Line Adapter or
USB Source
Most USB charging applications limit charging cur-
rent to 500mA due to the limitations of a USB port
as a power source. The AAT3685 is capable of,
and may be programmed for, constant current
charge levels up to 1A. Thus, charging operation
is not just restricted to use with USB port supplies.
Any power source may be used within the operat-
ing voltage limits as specified in the Electrical
Characteristics section of this datasheet. This
makes the AAT3685 perfect for applications that
only have one input path, but may access either a
line adapter source or a USB port supply.
In order to fully utilize the power capacity from a line
adapter or USB port supply, program the SETH
charge rate according to the highest charging cur-
rent capacity of the two possible sources, providing
that neither supply exceeds 1A. A lower charge
level may be set with the SETL charge rate and
selection of the higher or lower charge rate is con-
trolled via the PWRSEL function. If the pro-
grammed charge rate is greater than the current
source capacity, there is little danger of system fail-
ure because the AAT3685 charge reduction loop
will activate to automatically reduce the charging
current and maintain a supply voltage set by the
CHR threshold. If the input supply is incapable of
maintaining an input voltage greater than the under-
voltage lockout level of the AAT3685, the charge
control will suspend charging until the source sup-
ply is capable of supplying the minimum input cur-
rent to charge. At this point, the AAT3685 will auto-
matically resume charging in the appropriate mode
based on the battery cell voltage. In case of an
over-temperature condition with a high charge cur-
rent and large input-to-battery voltage difference,
the device will cycle from charging to thermal shut-
down and re-charge after temperature drops suffi-
ciently, until the battery is charged to 4.2V.
Enable / Disable
The AAT3685 provides an enable function to con-
trol the charger IC on and off. The enable (EN) pin
is an active high. When pulled to a logic low level,
the AAT3685 will be shut down and forced into the
sleep state. Charging will be halted regardless of
the battery voltage or charging state. When the
device is re-enabled, the charge control circuit will
automatically reset and resume charging functions
with the appropriate charging mode based on the
battery charge state and measured cell voltage.
Programming Charge Current
The fast charge constant current charge level for the
ADP/USB input is programmed with set resistors
placed between the SETH and SETL pins and
ground. The accuracy of the fast charge, as well as
the preconditioning trickle charge current, is domi-
nated by the tolerance of the set resistors used. For
this reason, 1% tolerance metal film resistors are
recommended for programming the desired con-
stant current level.
The fast charge constant current charge control
provides for two current set levels, SETH and
SETL. The PWRSEL pin is used to select the high
or low charge current levels. When the PWRSEL
pin is pulled to a voltage level above the V_PWRSEL(H)
threshold, the SETH current level will be selected.
Conversely, this pin should be pulled below the
V_PWRSEL(L) to enable the SETL charge level. These
two charge levels may be set to any level between
50mA and 1A, depending upon the system design
requirements for a given charge application. Refer
to Table 1 and Figure 3 for recommended R_SETH
and R_SETL values.
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3685.2006.10.1.3