AAT1205 Datasheet, PDF (15/21 Pages) Advanced Analog Technology, Inc. – 400-mA MULTI-INPUT LOW-DROPOUT REGULATOR WITH DUAL OUTPUT POWER MANAGEMENT

Advanced Analog Technology, Inc.
Thermal Information
AAT1205
To ensure reliable operation of the device, the junction temperature of the output device must be within the
safe operating area SOA . This is achieved by having a means to dissipate the heat generated from the
junction of the output structure. There are two components that contribute to thermal resistance. They
consist of two paths in series. The first path is the junction to case thermal resistance, R_JC; the second path is
the case to ambient thermal resistance, R_CA. The overall junction to ambient thermal resistance, R_JA, is
determined by
R_JA R_JC R_CA
Package and board layout incorporated in the application determines the ability to efficiently dissipate the
heat from the junction. The operating junction temperature is determined by the operation ambient
temperature, T_C, and the junction power dissipation, P_J.
The junction temperature, T_J, is equal to the following thermal equation
T_J T_C P_J R_JC
T_J T_C P_J R_JA
P_J R_CA
The AAT1205 is housed in a thermal enhanced package where the power pad is located in the bottom of the
device. When the power pad is soldered on a double-sided printed circuit board with two square inches of
copper allocated for "heat spreading", the resulting θ_JA is 50 /W. Hence, the maximum power dissipation
allowable for an operating ambient temperature of 70 , and a maximum junction temperature of 150 is
determined as
P_J T_J T_C / R_JA
P_J 150 70 /50 1.6W
Worst case maximum power dissipation is determined by
P_d 5.5 2.375 ×0.3+(5.5-3.135) ×0.1 0.0.9375+0.2365=1.174W
Normal operating maximum power dissipation is
P_d 5 2.5 ×0.3+(5-3.3) ×0.1 0.75+0.17=0.92W
Note: All thermal characteristics of the AAT1205 were measured using a double-sided board with two
square inches of copper area connected to the GND pins for "heat spreading". The use of multi-layer
board construction with power planes will further enhance the thermal performance of the package.
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