OPA2211-EP_16 Datasheet, PDF (18/32 Pages) Texas Instruments – Low-Power, Precision Operational Amplifier

OPA2211-EP
SBOS761 – NOVEMBER 2015
Application Information (continued)
R_F
www.ti.com
R_I
-In
+In
I_D
V_IN(1)
+V_S
+V
OPA2211-EP
Op-Amp
Core
ESD Current-
Steering Diodes
Out
Edge-Triggered ESD
Absorption Circuit
R_L
-V
-V_S
(1) V_IN = +V_S + 500 mV
Figure 40. Equivalent Internal ESD Circuitry and its Relation to a Typical Circuit Application
Figure 40 depicts a specific example where the input voltage, V_IN, exceeds the positive supply voltage (+V_S) by
500mV or more. Much of what happens in the circuit depends on the supply characteristics. If +V_S can sink the
current, one of the upper input steering diodes conducts and directs current to +V_S. Excessively high current
levels can flow with increasingly higher V_IN. As a result, the data sheet specifications recommend that
applications limit the input current to 10mA.
If the supply is not capable of sinking the current, V_IN may begin sourcing current to the operational amplifier, and
then take over as the source of positive supply voltage. The danger in this case is that the voltage can rise to
levels that exceed the operational amplifier absolute maximum ratings. In extreme but rare cases, the absorption
device triggers on while +V_S and –V_S are applied. If this event happens, a direct current path is established
between the +V_S and –V_S supplies. The power dissipation of the absorption device is quickly exceeded, and the
extreme internal heating destroys the operational amplifier.
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 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.
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