AAT1205 AAT, AAT1205 Datasheet - Page 15

• Manufacturer Part Number: AAT1205
• Description: MULTI-INPUT LOW-DROPOUT REGULATOR
• Manufacturer: AAT

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, R
the case to ambient thermal resistance, R
determined by ：
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
The junction temperature, T
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
allowable for an operating ambient temperature of 70 , and a maximum junction temperature of 150
determined as ：
Worst case maximum power dissipation is determined by ：
Normal operating maximum power dissipation is ：
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.
T
T
P
P
P
P
R
J
J
d
d
J
J
＝（ T
＝（ 150 － 70 ） /50 ＝ 1.6W
＝ T
＝ T
＝（ 5.5 － 2.375 ） ×0.3+(5.5-3.135) ×0.1 ＝ 0.0.9375+0.2365=1.174W
＝（ 5 － 2.5 ） ×0.3+(5-3.3) ×0.1 ＝ 0.75+0.17=0.92W
JA
＝ R
C
, and the junction power dissipation, P
C
C
＋ P
＋ P
JC
J
－ T
Advanced Analog Technology, Inc.
＋ R
J
J
（ R
（ R
C
CA
） / R
JC
JA
–
）＋ P
）
J
–
, is equal to the following thermal equation ：
JA
Advanced Analog Technology, Inc
台灣類比科技股份有限公司
J
（ R
CA
）
CA
. The overall junction to ambient thermal resistance, R
Page 15 of 21
JA
J
℃
.
is 50 /W. Hence, the maximum power dissipation
℃
.
–
–
JC
; the second path is
V 1.0
AAT1205
JA
℃
, is
is