2 Understanding EOS

The Industry Council on ESD defines electrical overstress [3] as “when a maximum limit for either the voltage across, the current through, or the power dissipated in the device is exceeded and causes immediate damage or malfunction, or latent damage resulting in an unpredictable reduction of its lifetime.” Of these conditions, it is the overvoltage that can open unintended current paths such as forward or reverse breakdown of diodes or oxides reaching their breakdown voltage within integrated circuits (ICs). Once an overvoltage opens an unintended current path, the resulting currents can cause damage that includes the melting of silicon; the fusing of metal interconnects; thermal damage to packaging material; and the fusing of bond-wires, leading to electrically induced physical damage (EIPD).

It is possible to relate EOS to the absolute maximum ratings specific to the voltage ratings of a device:

• Region A: The safe operating area.
• Region B: No guarantee on device functionality or parameter specifications. Although physical damage is not expected, extended operation may have reliability issues.
• Region C: Beyond the absolute maximum ratings, there is a severe degradation in device lifetime, and a risk of latent failure.
• Region D: Expected to suffer immediate physical damage.

As Figure 1 illustrates, you should expect problems when the device operates beyond the absolute maximum rating. That’s why suppressing transient overvoltages beyond the absolute maximum rating requires protection.