Micrel, Inc. MIC5265
February 2007 10
M9999-022307
MIC5265 Junction-To-Ambient Thermal Resistance
Package
θ
JA
Recommended
Minimum Footprint
θ
JA
1” Sq.
Copper Clad
θ
JC
SOT-23-5
(M5 or D5)
235°C/W 125°C 145°C/W
Thermal Resistance
Substituting PD for PD(max) and solving for the ambient
operating temperature will give the maximum operating
conditions for the regulator circuit. The junction-to-
ambient thermal resistance for the minimum footprint is
235C/W. The maximum power dissipation must not be
exceeded for proper operation.
For example, when operating the MIC5265-2.8YD5 at an
input voltage of 5.0V at 150mA with a minimum footprint
layout, the maximum ambient operating temperature TA
can be determined as follows:
WC
TC
W
A
/235
125
33.0
°
−°
=
TA = 47.45°C
Therefore, a 2.8V application at 150mA of output current
can accept an ambient operating temperature of 47°C in
a SOT-23-5 package. For a full discussion of heat
sinking and thermal effects on voltage regulators, refer
to the “Regulator Thermals” section of Micrel’s Designing
with Low-Dropout Voltage Regulators handbook. This
information can be found on Micrel's website at:
http://www.micrel.com/_PDF/other/LDOBk_ds.pdf
