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
OPA1641
R
S
(3)
TVS
(2)
TVS
(2)
OPA1641
OPA1642
OPA1644
www.ti.com SBOS484B –DECEMBER 2009–REVISED AUGUST 2010
Another common question involves what happens to If there is an uncertainty about the ability of the
the amplifier if an input signal is applied to the input supply to absorb this current, external zener diodes
while the power supplies +V
S
and/or –V
S
are at 0V. may be added to the supply pins as shown in
Again, it depends on the supply characteristic while at Figure 35. The zener voltage must be selected such
0V, or at a level below the input signal amplitude. If that the diode does not turn on during normal
the supplies appear as high impedance, then the operation. However, its zener voltage should be low
operational amplifier supply current may be supplied enough so that the zener diode conducts if the supply
by the input source via the current steering diodes. pin begins to rise above the safe operating supply
This state is not a normal bias condition; the amplifier voltage level.
most likely will not operate normally. If the supplies
are low impedance, then the current through the
steering diodes can become quite high. The current
level depends on the ability of the input source to
deliver current, and any resistance in the input path.
(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 © 2009–2010, Texas Instruments Incorporated 15
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