Regarding using the LD39050PU33R voltage regulator which is 5V to 3.3V fixed voltage regulator without any heatsink, its maximum current is given as 500mA. I was trying to figure out how they calculated this 500mA. So I tried to calculate the maximum current by myself by using the thermal resistances and maximum junction temperature as follows:
For 5V input the voltage drop across the regulator will be Vd = 5V-3.3V = 1.7V.
Max junction temperature is 125°C. And in the worse case if we have 55°C ambient temperature the ΔT = 70°C.
That means maximum power dissipated Pd can be found from:
ΔT = Pd * R_jc
Pd = 70 / 65 = 1.077W
This makes the max current I = Pd / Vd then I = 1.077 / 1.7 = 633mA.
In my calculation I took max ambient temperature 55°C. To obtain 500mA, the ambient temperature would be taken as around 70°C. Is my conclusion correct?