OPA140_15 Datasheet, PDF (21/44 Pages) Texas Instruments – High-Precision, Low-Noise, Rail-to-Rail Output,11-MHz JFET Op Amp

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OPA140, OPA2140, OPA4140
SBOS498B – JULY 2010 – REVISED NOVEMBER 2015
Feature Description (continued)
Another common question involves what happens to the amplifier if an input signal is applied to the input while
the power supplies +V_S 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.
(2)
TVS
R_F
I_D
V_IN(1)
R_I
-In
(3)
R_S
+In
+V_S
+V
OPA140
Op Amp
Core
ESD Current-
Steering Diodes
Out
Edge-Triggered ESD
Absorption Circuit
R_L
-V
-V_S
(2)
TVS
(1) V_IN = +V_S + 500 mV.
(2) TVS: +V_S(max) > V_{TVSBR (Min)} > +V_S
(3) Suggested value approximately 1 kΩ.
Figure 37. Equivalent Internal ESD Circuitry and Its Relation to a Typical Circuit Application
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