OPA1641 Datasheet, PDF (23/31 Pages) Texas Instruments – High-Performance, JFET-Input AUDIO OPERATIONAL AMPLIFIERS

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OPA1641, OPA1642, OPA1644
SBOS484C – DECEMBER 2009 – REVISED DECEMBER 2015
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 0 V. Again, it depends on the supply characteristic while at 0 V, 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 through 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.
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 37. 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 37. Equivalent Internal ESD Circuitry and the Relation to a Typical Circuit Application
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