Overcoming Amplifier Electrical Overstress Problems
by Thomas Kuehl and Bonnie C Baker, Senior Applications Engineers, Texas Instruments Incorporated
A common question from operational amplifier (op amp) users is, “Can the voltage inputs of an amplifier be higher than the power supply rail?” This might occur if there are multiple power sources in a system. If these supplies are turned on at different times, a pin or pins of a device in the system might be subjected to an over-voltage condition. This would expose the device to an electrical overstress (EOS) event. Another overstress scenario is if a signal from the “outside-world” or from a separate part of a system, under different power, appears on the input or output of an op amp.
If you want to design systems that are reliable, easy to manufacture, with low-latent field-failures, read on. In this TechNote we will look at this issue from two perspectives. When we think of an amplifier being subjected to an EOS condition, we might think of an electrostatic discharge (ESD) event. The ESD event exposes the amplifier’s pins to a short duration, high-voltage, discharge event. The second (often overlooked) overstress condition is an EOS event. An EOS event exposes the amplifier to lower overvoltages and currents compared to an ESD event, but lasts longer. By the end of this TechNote you will have an understanding of potential amplifier EOS conditions and a game plan for attacking them. With this plan you will be armed to design a robust system outside the integrated circuit that will prevent electrical overstress damage.
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