AAT3692 Datasheet, PDF (16/19 Pages) Skyworks Solutions Inc. – Dual Input 1.6A Linear Charger with 28V OVP in a 3x4 TDFN Package

DATA SHEET
AAT3692
Dual Input 1.6A Linear Charger with 28V OVP in a 3x4 TDFN Package
Thermal Considerations
The actual maximum charging current is a function of the
charge input voltage (USBCH and ADPCH), the battery
voltage at the BAT pin, the ambient temperature, the ris-
ing temperature when charge current passing through the
R_DS(ON) of the charging pass, and the thermal impedance
of the package. The maximum programmable current
may not be achievable under all operating parameters.
The AAT3692 is offered in a 3x4mm TDFN package which
can provide up to 2.0W of power dissipation when prop-
erly soldered to a printed circuit board and has a maxi-
mum 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 char-
ger IC package in proximity to other heat generating
devices in a given application design. The ambient tem-
perature 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 = [(V_IN - V_BAT) · I_CC + (V_IN · I_OP)]
P_D = Total power dissipation of the AAT3692
V_IN = V_ADP or V_USB, depending on which mode is selected
V_BAT = Battery voltage at the BAT pin
I_CC = Maximum constant fast charge current
programmed for the application
I_OP = Quiescent current consumed by the charger IC for
normal operation.
Next, the maximum operating ambient temperature for
a given application can be estimated based on the ther-
mal resistance of the 3x4 TDFN package when suffi-
ciently mounted to a PCB layout and the internal thermal
loop temperature threshold.
Where:
T_A = T_J - (θ_JA · P_D)
T_A = Ambient temperature in °C
T_J = Maximum device junction temperature below the
thermal loop threshold
P_D = Total power dissipation by the device
θ_JA = Package thermal resistance in °C/W.
Example:
For an application where the fast charge current for the
adapter mode is set to 1A, V_ADP = 5.0V, and the worst
case battery voltage is 3.6V, what is the maximum ambi-
ent temperature at which the digital thermal loop limit-
ing will become active?
Given:
V_ADP = 5.0V
V_BAT = 3.6V
I_CC = 1A
I_OP = 0.25mA
T_J = 110°C
θ_JA = 50°C/W
The device power dissipation for the stated condition can
be calculated as below:
P_D = (5.0 – 3.6V) · 1A + (5.0V · 0.25mA) ≈ 1.4W
The maximum ambient temperature is
T_A = 110°C - (50°C/W · 1.4W) = 40°C
Therefore, under the stated conditions for this worst
case power dissipation example, the AAT3692 will enter
the digital thermal loop and lower the fast charge con-
stant current when the ambient operating temperature
rises above 40°C.
Printed Circuit Board
Layout Considerations
For the best results, it is recommended to physically place
the battery pack as close to the AAT3692 BAT pin as pos-
sible. To minimize voltage drops on the PCB, keep the
high current carrying traces adequately wide. For maxi-
mum power dissipation of the AAT3692 TDFN package,
the exposed pad should be soldered to the board ground
plane to further increase local heat dissipation. A ground
pad below the exposed pad is strongly recommended.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201895B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 27, 2012