Question
Are you sure that ADP2108 can withstand +125°C of Operating Ambient Temperature Range at full load no matter of the power dissipation of the device,and the junction-to-ambient thermal resistance of the package?
Or there is a mistake in the datasheet?
Answer
That’s not right. The more critical temperature of the part is definitely the Junction Temperature. Also monitoring the ambient temperature does notguarantee that the Junction temperature is within the specified limits. In applications with high power dissipation and poor thermal resistance, themaximum ambient temperature may have to be derated. In applications with moderate power dissipation and low PCB thermal resistance, the maximumambient temperature can exceed the maximum limit as long as the junction temperature is within specification limits.The junction temperature (TJ) of the device is dependent on the ambient temperature (TA), the power dissipation (PD) of the device, and thejunction-to-ambient thermal resistance of the package (èJA). Maximum junction temperature (TJ) is calculated from the ambient temperature (TA) andpower dissipation (PD) using the formulaTJ = TA + (PD × èJA).
This is also stated in the ADP2108 (http://www.analog.com/ADP2108) datasheet on page 4.