Advanced Analog Technology, Inc.
Thermal Information
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, RJC; the
second path is the case to ambient thermal resistance, RCA. The overall junction to ambient thermal
resistance, RJA, is determined by：
RJA＝RJC＋RCA
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, TC , and the junction power dissipation, PJ.
The junction temperature, TJ, is equal to the following thermal equation：
TJ＝TC ＋PJ（RJC）＋PJ（RCA）
TJ＝TC ＋PJ（RJA）
This particular application uses the 8-pin SOIC package with standard lead frame with a dedicated
ground terminal. Hence, the maximum power dissipation allowable for an operating ambient
temperature of 70℃, and a maximum junction temperature of 150℃ is determined as：
PJ＝（TJ－TC ）/ RJA
PJ＝（150－70）/70＝1.1W
Worst case maximum power dissipation is determined by：
Pd ＝（5.5－3.135）×0.25＝0.591W
Normal operating maximum power dissipation is：
Pd ＝（5－3.3）×0.25＝0.425W
Note: The thermal characteristics of the AAT1203 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.
– 台灣類比科技股份有限公司 –
– Advanced Analog Technology, Inc. –
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