AD8421 Common Design Pitfalls to Avoid

Document created by analog-archivist Employee on Feb 23, 2016
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What are common pitfalls to avoid while designing with AD8421?


AD8421 is a high performance precision instrumentation amplifier, and as such,
face certain situations for which it is unsuitable.  One of the most useful
illustrations in the datasheet is the Vout vs. Vcm plot, which shows the
optimum operating condition for the AD8421.  Using the AD8421 outside of the
recommended region may lead to internal node saturation, and subsequent loss of

Instrumentation amplifiers are not isolated, and therefore cannot measure
floating voltages.  A ground reference must be present.
AD8421’s output is generated relative to a REF voltage.  This REF input should
be driven by a low-Z source.
The AD8421 datasheet has a comprehensive “THEORY OF OPERATION” section that
details how to get the best performance from this product, and how to avoid
common pitfalls.