AAT3683_12 Datasheet, PDF (16/22 Pages) Skyworks Solutions Inc. – 1A Linear Li-Ion Battery Charger

Most of the commonly used NTC thermistors in battery
packs are approximately 10k 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 within 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
thermistor 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 10k
resistor. Alternatively, on the AAT3683-2 only, the TS pin
may be left open.
For AAT3683-4, the internal battery temperature 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 characteris-
tics table in this datasheet, the TS1 threshold = 0.30 · V_IN
and the TS2 threshold = 0.60 · V_IN. If the use of the TS
pin function is not required on AAT3683-4, the TS pin
should be connected to input supply VIN.
V_IN
IN
AAT3683-4
0.60x V_IN
TS
Battery Cold Fault
Battery
Pack
x V_IN
Battery Hot Fault
Figure 3: AAT3683-4 Battery Temperature Sense
Circuit.
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
DATA SHEET
AAT3683
1A Linear Li-Ion Battery Charger
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 situa-
tion should be calculated:
Where:
P_D(MAX) =
T_J - T_A
Θ_JA
P_D(MAX) = Maximum Power Dissipation (W)
_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 dis-
sipation 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.
Next, the power dissipation can be calculated by the fol-
lowing equation:
P_D = (V_IN - V_BAT) · I_CH + V_IN · I_OP
Where:
P_D = Total Power Dissipation by the Device
V_IN = Input Voltage
V_BAT = Battery Voltage as Seen at the BAT Pin
I_CH = Constant Charge Current Programmed for the
Application
I_OP = Quiescent Current Consumed by the Charger IC
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
16
201885B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012