AAT3783_12 Datasheet, PDF (16/20 Pages) Skyworks Solutions Inc. – 1-A Linear Li-Ion/Polymer Battery Charger with 28V Over-Voltage Protection

DATA SHEET
AAT3783
1-A Linear Li-Ion/Polymer Battery Charger with 28V Over-Voltage Protection
istors in battery packs are approximately 10kΩ at room
temperature (25°C). The TS pin 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
AAT3783 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 ter-
minated to ground using a 10kΩ resistor. Alternatively,
on the AAT3783, the TS pin may be left open.
Over-Temperature Shutdown
The AAT3783 has a thermal protection control circuit
which will shut down charging functions should the inter-
nal die temperature exceed the preset thermal limit
threshold. Once the internal die temperature falls below
the thermal limit, normal operation will resume the pre-
vious charging state.
Digital 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_{CH_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 AAT3783 will always provide the highest
level of constant current in the fast charge mode possible
for any given ambient temperature condition.
Thermal Considerations
and High Output Current Applications
The AAT3783 is designed to deliver a continuous charg-
ing current. The limiting characteristic for maximum safe
operating charging current is its package power dissipa-
tion. Many considerations should be taken into account
when designing the printed circuit board layout, as well
as the placement of the IC package in proximity to other
heat generating devices in a given application design.
The ambient temperature around the 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(MAX) - 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 (°C) [115ºC]
T_A = Ambient Temperature (°C)
Figure 3 shows the relationship of maximum power dis-
sipation and ambient temperature of AAT3783.
2.5
2
1.5
1
0.5
0
0
25
50
75
100
T_A (°C)
Figure 3: Maximum Power Dissipation Before
Entering Digital 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)]
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201903B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 27, 2012