Datasheet

R
F
Op-Amp
Core
R
I
R
L
V
(1)
IN
I
D
-In
Out
+In
ESDCurrent-
SteeringDiodes
Edge-TriggeredESD
AbsorptionCircuit
+V
S
+V
-V
-V
S
OPA211
OPA211
OPA2211
SBOS377G – OCTOBER 2006 – REVISED MAY 2009 ...................................................................................................................................................... www.ti.com
(1) V
IN
= +V
S
+ 500mV.
Figure 49. Equivalent Internal ESD Circuitry and Its Relation to a Typical Circuit Application
An ESD event produces a short duration,
Figure 49 depicts a specific example where the input
high-voltage pulse that is transformed into a short
voltage, V
IN
, exceeds the positive supply voltage
duration, high-current pulse as it discharges through
(+V
S
) by 500mV or more. Much of what happens in
a semiconductor device. The ESD protection circuits
the circuit depends on the supply characteristics. If
are designed to provide a current path around the
+V
S
can sink the current, one of the upper input
operational amplifier core to prevent it from being
steering diodes conducts and directs current to +V
S
.
damaged. The energy absorbed by the protection
Excessively high current levels can flow with
circuitry is then dissipated as heat.
increasingly higher V
IN
. As a result, the datasheet
When an ESD voltage develops across two or more specifications recommend that applications limit the
of the amplifier device pins, current flows through one input current to 10mA.
or more of the steering diodes. Depending on the
If the supply is not capable of sinking the current, V
IN
path that the current takes, the absorption device
may begin sourcing current to the operational
may activate. The absorption device has a trigger, or
amplifier, and then take over as the source of positive
threshold voltage, that is above the normal operating
supply voltage. The danger in this case is that the
voltage of the OPA211 but below the device
voltage can rise to levels that exceed the operational
breakdown voltage level. Once this threshold is
amplifier absolute maximum ratings. In extreme but
exceeded, the absorption device quickly activates
rare cases, the absorption device triggers on while
and clamps the voltage across the supply rails to a
+V
S
and – V
S
are applied. If this event happens, a
safe level.
direct current path is established between the +V
S
When the operational amplifier connects into a circuit and – V
S
supplies. The power dissipation of the
such as that illustrated in Figure 49 , the ESD absorption device is quickly exceeded, and the
protection components are intended to remain extreme internal heating destroys the operational
inactive and not become involved in the application amplifier.
circuit operation. However, circumstances may arise
Another common question involves what happens to
where an applied voltage exceeds the operating
the amplifier if an input signal is applied to the input
voltage range of a given pin. Should this condition
while the power supplies +V
S
and/or – V
S
are at 0V.
occur, there is a risk that some of the internal ESD
Again, it depends on the supply characteristic while at
protection circuits may be biased on, and conduct
0V, or at a level below the input signal amplitude. If
current. Any such current flow occurs through
the supplies appear as high impedance, then the
steering diode paths and rarely involves the
operational amplifier supply current may be supplied
absorption device.
by the input source via the current steering diodes.
This state is not a normal bias condition; the amplifier
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