AAT3681
USB Port or AC Adapter
Lithium-Ion/Polymer Battery Charger
Application Information
Nominal
Set Resistor
Ω
ICHARGE (mA)
Value (k )
Adapter or USB Power Input
300
250
200
150
100
50
5.36
6.49
8.06
10.7
16.2
31.6
38.3
53.6
78.7
105
Constant current charge levels up to 300mA may
be programmed by the user when powered from a
sufficient input power source. The AAT3681 will
operate from the adapter input over a 4.0V to 6.5V
range. The constant current fast charge current for
the adapter input is set by the RSET resistor con-
nected between ISET and ground. Refer to Table 1
for recommended RSET values for a desired con-
stant current charge level.
40
30
20
15
Adapter Input Charge Inhibit and Resume
Table 1: RSET Values.
The AAT3681 has a UVLO and power on reset fea-
ture so that if the input supply to the ADP pin drops
below the UVLO threshold, the charger will sus-
pend charging and shut down. When power is re-
applied to the ADP pin or the UVLO condition
recovers, 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.
1000
100
10
1
Enable / Disable
1
10
100
1000
The AAT3681 provides an enable function to con-
trol the charger IC on and off. The enable (EN) pin
is internally pulled down. When pulled to a logic
high level, AAT3681 is enabled. When left open or
pulled to a logic low level, the AAT3681 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 on the BAT pin.
RSET (kΩ)
Figure 2: Constant Charging Current
vs. Set Resistor Values.
Protection Circuitry
Over-Voltage Protection
An over-voltage event is defined as a condition
where the voltage on the BAT pin exceeds the
maximum battery charge voltage and is set by the
over-voltage protection threshold (VOVP). If an over-
voltage condition occurs, the AAT3681 charge con-
trol will shut down the device until voltage on the
BAT pin drops below VOVP. The AAT3681 will
resume normal charging operation after the over-
voltage condition is removed.
Programming Charge Current
The fast charge constant current charge level is
user programmed with a set resistor placed
between the ISET pin and ground. The accuracy of
the fast charge, as well as the preconditioning trick-
le charge current, is dominated by the tolerance of
the set resistor used. For this reason, a 1% toler-
ance metal film resistor is recommended for the set
resistor function. Fast charge constant current lev-
els from 15mA to 300mA may be set by selecting
the appropriate resistor value from Table 1.
Over-Temperature Shutdown
The AAT3681 has a thermal protection control circuit
which will shut down charging functions should the
internal die temperature exceed the preset thermal
limit threshold. Once the internal die temperature
falls below the thermal limit, normal operation will
resume the previous charging state.
3681.2007.01.1.2
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
