Qi want to know if i will need a heat sink fro this device (Vin=3.3V and
Iout=100uA). Therefore, i need to know what are the Tj, Tjunction-ambient and
can you send me those parameters?
AThe thetaJA for the sot 23 package used by the AD1582 is 300degC/W. A max
junction temperature of 125degC is a good assumption for this device.
Total power consumption is 3.3V x 65uA + (3.3V – 2.5V) x 100uA = 214uW + 80uW =
Expected junction temperature rise above ambient = 300degC/W x 280uW = 0.08degC
As you can see the power dissipation in the AD1582 even when sourcing 100uA is
so low that the rise in junction temperature will be less than 1degC. A heat
sink should not be required in such conditions.
As an aside, note that the thetaJA we quote on the datasheet (usually found in
the absolute maximum ratings sections) uses a “SEMI standard board” under still
air conditions according to SEMI standard G38-87. This assumes a large copper
area ground plane approx 2inch x 2 inch which acts as a heat sink. The area of
adjacent ground plan and the width of PCB track which used to connect the
component pad can all affect the thermal resistance of the package.