Datasheet

R
F
OpAmp
Core
R
I
R
L
V
(1)
IN
I
D
-In
Out
+In
ESDCurrent-
SteeringDiodes
Edge-TriggeredESD
AbsorptionCircuit
+V
S
+V
-V
-V
S
OPA141
R
S
(3)
TVS
(2)
TVS
(2)
OPA141
OPA2141
OPA4141
www.ti.com SBOS510B –MARCH 2010–REVISED MAY 2010
Figure 35 depicts a specific example where the input Again, it depends on the supply characteristic while at
voltage, V
IN
, exceeds the positive supply voltage 0V, or at a level below the input signal amplitude. If
(+V
S
) by 500mV or more. Much of what happens in the supplies appear as high impedance, then the
the circuit depends on the supply characteristics. If operational amplifier supply current may be supplied
+V
S
can sink the current, one of the upper input by the input source via the current steering diodes.
steering diodes conducts and directs current to +V
S
. 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
increasingly higher V
IN
. As a result, the datasheet 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.
If the supply is not capable of sinking the current, V
IN
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 35. 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
while the power supplies +V
S
and/or –V
S
are at 0V. that the zener diode conducts if the supply pin begins
to rise above the safe operating supply voltage level.
(1) V
IN
= +V
S
+ 500mV.
(2) TVS: +V
S(max)
> V
TVSBR (Min)
> +V
S
(3) Suggested value approximately 1kΩ.
Figure 35. Equivalent Internal ESD Circuitry and Its Relation to a Typical Circuit Application
Copyright © 2010, Texas Instruments Incorporated 17
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