MS-2251_15 Datasheet, PDF (1/6 Pages) Analog Devices – Technical Article

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Data Sheet Intricacies—
Absolute Maximum Ratings
and Thermal Resistances
by Vicky Wong, Applications Engineer,
Analog Devices, Inc.
Technical Article
MS-2251
TELL ME MORE ABOUT THE ABSOLUTE MAXIMUM
RATINGS.
The absolute maximum ratings table contains maximum
limits for voltage, temperature, and allowed current.
IDEA IN BRIEF
Frequently asked questions about absolute maximum
ratings and thermal resistances are answered.
Op amps that do not function as expected can be
very frustrating to the users. There are many ways
to build a successful circuit design, but there are
even more ways to break one. Unfortunately, 90% of the
problems/issues/failures that users face arise from careless or
incorrect reading of the data sheet. Here are a couple of
frequently asked questions on absolute maximum ratings
and thermal resistances that may seem to have obvious
answers but yet are often misinterpreted by the general
audience.
IS IT ALRIGHT TO OPERATE MY AMPLIFIER
SLIGHTLY ABOVE THE ABSOLUTE MAXIMUM
RATINGS?
Absolutely not! It is critical to adhere to the absolute
maximum ratings in a data sheet to avoid damaging the part
permanently. The absolute maximum ratings indicate the
limits that a device can tolerate, but not operate at. For
example, having an input voltage greater than the absolute
maximum causes the input differential pairs of the op amp
to breakdown leading to excessive fault current. This not
only results in a shift in parametric performance, but also
metal migration that over time, destroys the part
permanently. In short, keep away from the maximum
ratings, or there is a very high chance the part will be
destroyed!
Figure 1. Example Absolute Maximum Ratings Table
The maximum supply voltage that can be applied to an op
amp is determined by the fabrication process. It refers to the
instantaneous value, not the average or final value. Low
voltage CMOS op amps from Analog Devices, Inc., are
typically limited to 6 V, whereas high voltage bipolar parts
are limited to 36 V.
Maximum input voltage depends on the input stage
architecture and supply voltage of the op amp. Almost all op
amps are protected by ESD diodes. The input ESD diodes
determine how far the input voltage can go beyond the
supply voltage. Typically, input voltage is limited to one
diode drop (about 300 mV to 700 mV depending on the
temperature) beyond the supply rails. When the op amp is
operated out of the input voltage range, but within the
absolute maximum, its parametric performance changes. It
will not be damaged, but may not be functional, for example,
it may phase reverse, the input bias current, or the input
offset voltage may greatly increase. Once the input voltage
exceeds the absolute maximum, the op amp is exposed to
permanent damage. Users frequently face issues with having
December 2011 | Page 1 of 6
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