R

F

OpAmp

Core

R

I

R

L

V

(1)

IN

I

D

-In

Out

+In

ESDCurrent-

SteeringDiodes

Edge-TriggeredESD

AbsorptionCircuit

+V

S

+V

-V

-V

S

OPA140

R

S

(3)

TVS

(2)

TVS

(2)

OPA140

OPA2140, OPA4140

www.ti.com

SBOS498A – JULY 2010 – REVISED AUGUST 2010

Figure 38 depicts a specific example where the input

Again, it depends on the supply characteristic while at

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

the supplies appear as high impedance, then the

the circuit depends on the supply characteristics. If

operational amplifier supply current may be supplied

by the input source via the current steering diodes.

This state is not a normal bias condition; the amplifier

Excessively

high

current

levels

can

flow

with

most likely will not operate normally. If the supplies

are low impedance, then the current through the

specifications recommend that applications limit the

steering diodes can become quite high. The current

input current to 10mA.

level depends on the ability of the input source to

deliver current, and any resistance in the input path.

may

begin

sourcing

current

to

the

operational

If there is an uncertainty about the ability of the

amplifier, and then take over as the source of positive

supply to absorb this current, external zener diodes

supply voltage. The danger in this case is that the

may be added to the supply pins as shown in

voltage can rise to levels that exceed the operational

Figure 38. The zener voltage must be selected such

amplifier absolute maximum ratings.

that the diode does not turn on during normal

operation.

Another common question involves what happens to

the amplifier if an input signal is applied to the input

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.

(1)

(2)

(3)

Suggested value approximately 1k

Ω.

Figure 38. Equivalent Internal ESD Circuitry and Its Relation to a Typical Circuit Application

Copyright © 2010, Texas Instruments Incorporated

17

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