Pam3112, Application information – Diodes PAM3112 User Manual
Page 8
PAM3112
Document number: DSxxxxx Rev. 2 - 3
8 of 17
January 2013
© Diodes Incorporated
PAM3112
A Product Line of
Diodes Incorporated
Application Information
(cont.)
Thermal Considerations
Where T
J(MAX)
is the maximum allowable junction temperature +125°C, T
A
is the ambient temperature and is the thermal resistance from the
junction to the ambient.
For example, as θ
JA
is 250°C/W for the SOT23 and TSOT25 packages based on the standard JEDEC 51-3 for a single-layer thermal test board,
the maximum power dissipation at T
A
= +25°C can be calculated by following formula:
(
)
W
4
.
0
250
/
C
25
C
125
P
)
MAX
(
D
=
°
−
°
=
SOT-23
It is also useful to calculate the junction temperature of the PAM3112 under a set of specific condition. Suppose the input voltage V
IN
=3.3V, the
output current I
O
=150mA and the case temperature T
A
= +40°C measured by a thermal couple during operation, the power dissipation is
defined as:
(
)
mW
315
A
70
*
V
3
.
3
mA
150
*
V
2
.
1
V
3
.
3
P
D
≅
μ
+
−
=
And the junction temperature, T
J
can be calculated as follows:
T
J
= T
A
+ P
D
*θ
JA
T
J
= 40°C +0.35W*250°C/W
= 40°C +78.75°C
= 118.75°C<T
J(MAX)
= +125°C
For this application, T
J
is lower than the absolute maximum operating junction temperature +125°C, so it is safe to use the PAM3112 in this
configuration.