OPA211_15 Datasheet, PDF (25/45 Pages) Texas Instruments – Low Power, Precision Operational Amplifier

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OPA211, OPA2211
SBOS377H – OCTOBER 2006 – REVISED NOVEMBER 2015
When an ESD voltage develops across two or more of the amplifier device pins, current flows through one or
more of the steering diodes. Depending on the path that the current takes, the absorption device may activate.
The absorption device has a trigger, or threshold voltage, that is above the normal operating voltage of the
OPA211 but below the device breakdown voltage level. Once this threshold is exceeded, the absorption device
quickly activates and clamps the voltage across the supply rails to a safe level.
When the operational amplifier connects into a circuit such as that shown in Figure 48, the ESD protection
components are intended to remain inactive and not become involved in the application circuit operation.
However, circumstances may arise where an applied voltage exceeds the operating voltage range of a given pin.
Should this condition occur, there is a risk that some of the internal ESD protection circuits may be biased on,
and conduct current. Any such current flow occurs through steering diode paths and rarely involves the
absorption device.
R_F
R_I
-In
+In
I_D
V_IN(1)
+V_S
+V
OPA211
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 48. Equivalent Internal ESD Circuitry and its Relation to a Typical Circuit Application
Figure 48 depicts a specific example where the input voltage, V_IN, exceeds the positive supply voltage (+V_S) by
500 mV 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 datasheet specifications recommend that applications
limit the input current to 10 mA.
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 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.
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