OPA211AI datasheet(18/37 Pages) TI1

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Op-Amp

Core

(1)

-In

Out

+In

ESDCurrent-

SteeringDiodes

Edge-TriggeredESD

AbsorptionCircuit

-V

-VS

OPA211

OPA2211

SBOS377G – OCTOBER 2006 – REVISED MAY 2009...................................................................................................................................................... www.ti.com

(1) VIN = +VS + 500mV.

Figure 49. Equivalent Internal ESD Circuitry and Its Relation to a Typical Circuit Application

ESD

event

produces

short

duration,

Figure 49 depicts a specific example where the input

high-voltage pulse that is transformed into a short

voltage, VIN, exceeds the positive supply voltage

duration, high-current pulse as it discharges through

(+VS) by 500mV or more. Much of what happens in

a semiconductor device. The ESD protection circuits

the circuit depends on the supply characteristics. If

are designed to provide a current path around the

+VS can sink the current, one of the upper input

operational amplifier core to prevent it from being

steering diodes conducts and directs current to +VS.

damaged. The energy absorbed by the protection

Excessively

high

current

levels

can

flow

with

circuitry is then dissipated as heat.

increasingly higher VIN. As a result, the datasheet

When an ESD voltage develops across two or more

specifications recommend that applications limit the

of the amplifier device pins, current flows through one

input current to 10mA.

or more of the steering diodes. Depending on the

If the supply is not capable of sinking the current, VIN

path that the current takes, the absorption device

may

begin

sourcing

current

the

operational

may activate. The absorption device has a trigger, or

amplifier, and then take over as the source of positive

threshold voltage, that is above the normal operating

supply voltage. The danger in this case is that the

voltage of the

OPA211

but

below

the

device

voltage can rise to levels that exceed the operational

breakdown voltage level. Once this threshold is

amplifier absolute maximum ratings. In extreme but

exceeded, the absorption device quickly activates

rare cases, the absorption device triggers on while

and clamps the voltage across the supply rails to a

+VS and –VS are applied. If this event happens, a

safe level.

direct current path is established between the +VS

When the operational amplifier connects into a circuit

and –VS supplies. The power dissipation of the

such as that illustrated in Figure 49, the ESD

absorption device is quickly exceeded, and the

protection

components

are

intended

remain

extreme internal heating destroys the operational

inactive and not become involved in the application

amplifier.

circuit operation. However, circumstances may arise

Another common question involves what happens to

where an applied voltage exceeds the operating

the amplifier if an input signal is applied to the input

voltage range of a given pin. Should this condition

while the power supplies +VS and/or –VS are at 0V.

occur, there is a risk that some of the internal ESD

Again, it depends on the supply characteristic while at

protection circuits may be biased on, and conduct

0V, or at a level below the input signal amplitude. If

current. Any such current flow

occurs

through

the supplies appear as high impedance, then the

steering

diode

paths

and

rarely

involves

the

operational amplifier supply current may be supplied

absorption device.

by the input source via the current steering diodes.

This state is not a normal bias condition; the amplifier

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