Power-Supply

ESD Cell

250

Ÿ

250

Ÿ

IN

±

IN+

TVS

+

±

TVS

+

8

OPA2156

SBOS900 – SEPTEMBER 2018

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Product Folder Links: OPA2156

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Copyright © 2018, Texas Instruments Incorporated

Feature Description (continued)

7.3.2 Electrical Overstress

Designers often ask questions about the capability of an operational amplifier to withstand electrical overstress.

These questions tend to focus on the device inputs, but can involve the supply voltage pins or even the output

pin. Each of these different pin functions have electrical stress limits determined by the voltage breakdown

characteristics of the particular semiconductor fabrication process and specific circuits connected to the pin.

Additionally, internal electrostatic discharge (ESD) protection is built into these circuits to protect them from

accidental ESD events both before and during product assembly.

A good understanding of this basic ESD circuitry and the relevance to an electrical overstress event is helpful.

Figure 2 illustrates the ESD circuits contained in the OPA2156 (indicated by the dashed line area). The ESD

protection circuitry involves several current-steering diodes connected from the input and output pins and routed

back to the internal power-supply lines, where the diodes meet at an absorption device internal to the operational

amplifier. This protection circuitry is intended to remain inactive during normal circuit operation.

Figure 2. Equivalent Internal ESD Circuitry Relative to a Typical Circuit Application

An ESD event produces a short-duration, high-voltage pulse that is transformed into a short-duration, high-

current pulse when discharging through a semiconductor device. The ESD protection circuits are designed to

provide a current path around the operational amplifier core to prevent damage. The energy absorbed by the

protection circuitry is then dissipated as heat.

When an ESD voltage develops across two or more amplifier device pins, current flows through one or more

steering diodes. Depending on the path that the current takes, the absorption device can activate. The absorption

device has a trigger, or threshold voltage, that is above the normal operating voltage of the OPA2156 but below

the device breakdown voltage level. When this threshold is exceeded, the absorption device quickly activates

and clamps the voltage across the supply rails to a safe level.