All operational amplifier (op amp) input stages feature some sort of protection against electrostatic discharge (ESD). Most amplifiers accomplish this with diodes from both inputs and the output to both supply rails. While these diodes offer protection against ESD strikes, the diodes can also lead to undesirable current through the ESD structure when one, or both, of the inputs exceeds the V+ rail. Fortunately, there are a select few op amps with an alternative input ESD structure designed to prevent this undesired current. This application report covers the standard ESD protection structure and an alternative ESD protection structure. The document also shows different testing methods for observing the behavior of the ESD protection under device shutdown and measurement data from devices with protection structures that do not have diodes from the inputs to the V+ supply pin.
All trademarks are the property of their respective owners.
To help deal with short-term, high-voltage events, amplifiers have electrostatic discharge (ESD) protection structures. These structures typically feature diodes that protect amplifier inputs and outputs from unintended damage by clamping these pins to the supply rails under ESD conditions.
However, these diodes are not designed to be relied upon for electrical overstress (EOS) events where the input voltage significantly exceeds the supply rail for a longer period of time. Under such a scenario, current can flow from the inputs to the supply rails. This can have undesirable effects including, but not limited to, back-powering the amplifier, device damage, and complete device failure. Understanding these scenarios and what can be done to avoid them is important in op amp circuit design.
This application note considers the standard amplifier ESD protection structure as well as an alternative structure that does not have diodes from the inputs to the V+ supply rail. Then, some Texas Instruments devices are highlighted with this alternative input protection structure and how the behavior of the protection structure of an op amp can be measured for certain scenarios.