1A Ultra Low Dropout Linear Regulator
Table. 1. Absolute Maximum Ratings of Thermal Resistance
No heat sink / No air flow / No adjacent heat source / T
A
= 25°C
Characteristic
Thermal Resistance Junction-To-Ambient / SOT-223
Thermal Resistance Junction-To-Ambient / TO-252
TJ4940
Symbol
θ
JA-SOT223
θ
JA-TO252
Rating
140
Unit
°C/W
°C/W
105
In case that there is no cooling solution and no heat sink / minimum copper plane area for heat sink, the
maximum allowable power dissipation of each package is as follow;
Characteristic
Maximum Allowable Power Dissipation at T
A
=25°C / SOT-223
Maximum Allowable Power Dissipation at T
A
=25°C / TO-252
Symbol
P
DMax-SOT223
P
DMax-TO252
Rating
0.714
0.952
Unit
W
W
- Please note that above maximum allowable power dissipation is based on the minimum copper
plane area which does not exceed the proper footprint of the package. And the ambient
temperature is
25°C.
If proper cooling solution such as heat sink, copper plane area, air flow is applied, the maximum allowable
power dissipation could be increased. However, if the ambient temperature is increased, the allowable
power dissipation would be decreased.
For example, in case of SOT-223 and TO-252 package,
θ
JA-SOT223
is 140 °C/W and
θ
JA-TO52
is 105 °C/W,
however, as shown in below graph,
θ
JA
could be decreased with respect to the copper plane area. So,
the specification of maximum power dissipation for an application is fixed, the proper copper plane area
could be estimated by following graphs. As shown in graph, wider copper plane area leads lower
θ
JA
.
Junction To Ambient Thermal Resistance,
θ
JA
vs. 1 ounce Copper Area [SOT-223 Package]
Junction To Ambient Thermal Resistance,
θ
JA
vs. 2 ounce Copper Area [TO-252 Package]
Apr. 2010 – Preliminary
7/8
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
