OPA1641_15 Datasheet, PDF (15/29 Pages) Texas Instruments – High-Performance, JFET-Input AUDIO OPERATIONAL AMPLIFIERS

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Another common question involves what happens to
the amplifier if an input signal is applied to the input
while the power supplies +V_S and/or –V_S are at 0V.
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
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
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.
OPA1641
OPA1642
OPA1644
SBOS484B – DECEMBER 2009 – REVISED AUGUST 2010
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 as shown in
Figure 35. 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.
TVS⁽²⁾
R_F
R_I
-In
R_S(3)
+In
I_D
V_IN(1)
+V_S
+V
OPA1641
Op-Amp
Core
ESD Current-
Steering Diodes
Out
Edge-Triggered ESD
Absorption Circuit
R_L
-V
-V_S
TVS⁽²⁾
(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
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