7.3.5 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 from accidental

ESD events both before and during product assembly.

Having a good understanding of this basic ESD circuitry and the relevance to an electrical overstress event is

helpful. Figure 7-4 shows an illustration of the ESD circuits contained in the OPAx186 (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.

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

current pulse while 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 greater than the normal operating voltage of the

OPAx186, but less than 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.

Figure 7-4 shows that when the operational amplifier connects into a circuit, the ESD protection components

are intended to remain inactive, and do not become involved in the application circuit operation. However,

circumstances can arise where an applied voltage exceeds the operating voltage range of a given pin. If this

condition occurs, there is a risk that some internal ESD protection circuits are biased on and conduct current.

Any such current flow occurs through steering-diode paths and rarely involves the absorption device.

Op Amp

Core

R

F

R

I

R

L

V

IN

(1)

I

D

IN

OUT

+IN

ESD Current-

Steering Diodes

V+

R

S

(3)

TVS

(2)

Edge-Triggered ESD

Absorption Circuit

V±

TVS

(2)

(1) VIN = (V+) + 500 mV

(2) TVS: 26 V > VTVSBR (min) > V+, where VTVSBR (min) is the minimum specified value for the transient voltage suppressor breakdown

voltage.

(3) Suggested value is approximately 5 kΩ in example overvoltage condition.

Figure 7-4. Equivalent Internal ESD Circuitry Relative to a Typical Circuit Application

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SBOS968B – JUNE 2022 – REVISED DECEMBER 2022

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