I am using a LM3480 on a board to generate a 3.3 V power supply with a 12 V power supply.
While testing several of my boards at 70°C, I have problems with some of them for which I was able to see on a scope the power output of this LM3480 falling down below the minimum power supply of the components it is expected to power up.
For an ambient temperature of TA=70°C, I measured a TC(max)=88°C on the LM3480.
Since, from the datasheet RθJA = 269.6°C/W and RθJC = 141.1°C/W, RθCA = RθJA - RθJC = 128.5°C/W.
I am then expecting to have P = (TC – TA) / RθCA = 140 mW and TJ = TA RθJA * P = TC RθJC * P = 107,76 °C.
Since the recommended temperature of the component is from TJ = -40°C to 125°C, I don't understand why its output is falling down.
Its consumption doesn't seem to be excessive as well.
Could you tell me if I missed something?