Many of our semiconductor products have ratings that are dependent on temperature. you many see something like Current-Continuous Drain (Id) @25°C and it shows a rating of 30mA(Tc) or 30mA(Tj>) ir 30mA(Ta). Often time customer do not understand what these rating mean. It gets even more confusing when manufactures list a rating similar to part BSZ034N04LSATMA1TR-ND which has a Current - Continuous Drain (Id) @ 25°C rating of 19A (Ta), 40A (Tc).
Here is a brief summary of these ratings:
Ta = Ambient temperature. This is a still air temperature reading for the environment that the semiconductor is in.
Tc = Case temperature. This is the temperature reading of the case of the semiconductor device.
Ta would normally mean the environment is cooled and kept at 25°C whereas Tc would mean the device is forcibly cooled through a directly attached heatsink and cooled to the 25°C.
Tj = Operating Junction temperature. This is the temperature of the device circuit itself under given conditions. Tj must be calculated from the Tc and/or Ta.
TJmax = Maximum Junction temperature. This is the maximum temperature that the device tolerate.