5 kW

Device

10 mA max

V+

V

IN

V

OUT

I

OVERLOAD

OPA2180

OPA4180

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SBOS584C – NOVEMBER 2011 – REVISED DECEMBER 2012

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 may 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.

These ESD protection diodes also provide in-circuit, input overdrive protection, as long as the current is limited to

10 mA as stated in the Absolute Maximum Ratings. Figure 29 shows how a series input resistor may be added to

the driven input to limit the input current. The added resistor contributes thermal noise at the amplifier input and

its value should be kept to a minimum in noise-sensitive applications.

Figure 29. Input Current Protection

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

current pulse as it discharges through a semiconductor device. The ESD protection circuits are designed to

provide a current path around the operational amplifier core to prevent it from being damaged. The energy

absorbed by the protection circuitry is then dissipated as heat.

When the operational amplifier connects into a circuit, the ESD protection components are intended to remain

inactive and not become involved in the application circuit operation. However, circumstances may arise where

an applied voltage exceeds the operating voltage range of a given pin. Should this condition occur, there is a risk

that some of the internal ESD protection circuits may be biased on, and conduct current. Any such current flow

occurs through ESD cells and rarely involves the absorption device.

If there is an uncertainty about the ability of the supply to absorb this current, external zener diodes may be

added to the supply pins. The zener voltage must be selected such that the diode does not turn on during normal

operation.

However, its zener voltage should be low enough so that the zener diode conducts if the supply pin begins to

rise above the safe operating supply voltage level.

Copyright © 2011–2012, Texas Instruments Incorporated

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