AAT3683 Datasheet, PDF (16/24 Pages) Advanced Analogic Technologies – 1A Linear Li-Ion Battery Charger

The AAT3683-2 checks battery temperature before
starting the charge cycle, as well as during all stages
of charging. This is accomplished by monitoring the
voltage at the TS pin. This system is intended for
use with negative temperature coefficient thermis-
tors (NTC) which are typically integrated into the bat-
tery package. Most of the commonly used NTC
thermistors in battery packs are approximately 10kΩ
at room temperature (25°C). The TS pin (3683-2
only) has been specifically designed to source 75µA
of current to the thermistor. The voltage on the TS
pin resulting from the resistive load should stay with-
in a window of 331mV to 2.39V. If the battery
becomes too hot during charging due to an internal
fault or excessive constant charge current, the ther-
mistor will heat up and reduce in value, pulling the
TS pin voltage lower than the TS1 threshold, and the
AAT3683-2 will stop charging until the condition is
removed, when charging will be resumed.
If the use of the TS pin function is not required by
the system, it should be terminated to ground using
a 10kΩ resistor. Alternatively, on the AAT3683-2,
the TS pin may be left open.
For AAT3683-3 and -4, the internal battery tempera-
ture sensing system is comprised of two comparators
which establish a voltage window for safe operation.
The thresholds for the TS operating window are
bounded by the TS1 and TS2 specifications.
Referring to the electrical characteristics table in this
datasheet, the TS1 threshold = 0.30 · V_IN and the TS2
threshold = 0.60 · V_IN.
VIN
IN
TS
Battery
Pack
AAT3683-3 and -4
0.60x VIN
Battery Cold Fault
Battery Hot Fault
x V_IN
Figure 3: AAT3683-3 and -4 Battery
Temperature Sense Circuit.
16
AAT3683
1A Linear Li-Ion Battery Charger
Thermal Considerations
The AAT3683 is offered in two packages
(STDFN2.2x2.2-10 and QFN33-16) both of which
can provide up to 2W of power dissipation when
properly bonded to a printed circuit board and have
a maximum thermal resistance of 50°C/W. Many
considerations should be taken into account when
designing the printed circuit board layout, as well
as the placement of the charger IC package in
proximity to other heat generating devices in a
given application design. The ambient temperature
around the charger IC will also have an effect on
the thermal limits of a battery charging application.
The maximum limits that can be expected for a
given ambient condition can be estimated by the
following discussion.
First, the maximum power dissipation for a given
situation should be calculated:
P_D(MAX) =
(T_J - T_A)
θ_JA
Where:
P_D(MAX) = Maximum Power Dissipation (W)
θ_JA
= Package Thermal Resistance (°C/W)
T_J
= Thermal Loop Entering Threshold (ºC)
[115ºC]
T_A
= Ambient Temperature (°C)
Figure 4 shows the relationship of maximum power
dissipation and ambient temperature of AAT3683.
2.5
2
1.5
1
0.5
0
0
25
50
75
100
T_A (°C)
Figure 4: Maximum Power Dissipation Before
Entering Thermal Loop.
\3683.2007.06.1.0