PAM3112 Datasheet, PDF (8/16 Pages) Power Analog Micoelectronics – 300mA CMOS Linear Regulator

Where T_J(MAX) is the maximum allowable junction
temperature 125°C, T_Ais the ambient temperature
and θ_JA is the thermal resistance from the junction
to the ambient.
For example, as θ_JA is 250°C/W for the SOT-23
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:
P = _D(MAX) (125°C-25°C)/250=0.4W 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
PAM3112
300mA CMOS Linear Regulator
thermal couple during operation, the power
dissipation is defined as:
P_D=(3.3V-1.2V)*150mA+3.3V*70μA≌315mW
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.
Power Analog Microelectronics,Inc
www.poweranalog.com
8
10/2008 Rev 1.3