Diodes PAM3101 - Manual (Page 12)

PAM3101
Document number: DSxxxxx Rev. 2 - 5
12 of 25
www.diodes.com
October 2012
© Diodes Incorporated
PAM3101
A Product Line of
Diodes Incorporated
Application Information
(cont.)
For example, as θ
JA is 250°C/W for the SOT-23 package and 180°C/W for the SOT-89 package 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
 
W 55 . 0 180 / C 25 C 125 P
) MAX ( D
    
SOT-89
It is also useful to calculate the junction temperature of the PAM3101 under a set of specific conditions. Suppose the input voltage V
IN
= 3.3V,
the output current I
O
= 300mA and the case temperature T
A
= +40°C measured by a thermalcouple during operation, the power dissipation for
the V
O
= 2.8V version of the PAM3101 can be calculated as:
 
mW 150 A 70 * V 3 . 3 mA 300 * V 8 . 2 V 3 . 3 P D
    
And the junction temperature, T
J
can be calculated as follows:
T
J
= T
A
+ P
D
* θ
JA
T
J
= 40°C +0.15W*250°C/W
= 40°C +37.5°C
= 77.5°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 PAM3101 in this
configuration.