AAT3691 Datasheet, PDF (15/18 Pages) Skyworks Solutions Inc. – Dual Input 1.6A Linear Charger with 28V OVP in a 3x4 TDFN Package

DATA SHEET
AAT3691
Dual Input 1.6A Linear Charger with 28V OVP in a 3x4 TDFN Package
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 AAT3691 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 AAT3691 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 AAT3691 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
201894B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 27, 2012
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