QPlease provide the junction temperature for the AD736ARZ as it is not shown in
the datasheet. Is the junction temperature the same as the storage temperature?
AAn estimation of the chip-junction temperature, TJ, can be obtained from the
following equation: TJ = TA + ( R θJA × PD )
where: TA = ambient temperature for the package ( °C )
R θJA = junction to ambient thermal resistance ( °C / W )
PD = power dissipation in package (W)There is no need to derate the AD736
because the junction temperature rise is extremely low, << 1°C above ambient,
and can be neglected. As you noted, the storage temperature is 125°C to 150°C
depending on package style, and the max operating is 70°C to 85°C. For an 8
lead SOIC operating at a 25°C ambient and ±5V, the temperature rise would be
155°C/W x 0.00016Ax10V or 0.248°C. In this case, the maximum operating
temperature is a function of the package, not the silicon, which is processed
at temperature >>400°C.
The standard practice for semiconductor products is to provide derating
guidelines if the life span of the product is degraded by temperature. This
condition doesn’t apply for low power devices because heat generated is
irrelevant to lifetime. Any relevant operating specifications affected by
temperature are listed in the data sheet.