Derating refers to thermal design in which the allowable power consumption is restricted according to the rise in the ambient temperature. A derating curve is a characteristics curve that indicates the total power dissipation (PT) vs. the ambient operating temperature (TA.)
When TA= +80°C in an 8-pin SOP (with PT = 440 mW and Rth (j - A) = 227°C/W @ TA = 25):
The characteristics for each package type are shown in the graphs below.
Remark If the diagonal lines of the derating curves are extended, the value at PT=0 is the maximum junction temperature (125°C in the case of operational amplifiers and comparators).