OPA211AIDRGR Datasheet, PDF (18/37 Pages) Texas Instruments – 1.1nV/√Hz Noise, Low Power, Precision Operational Amplifier in Small DFN-8 Package

OPA211
OPA2211
SBOS377G – OCTOBER 2006 – REVISED MAY 2009...................................................................................................................................................... www.ti.com
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 + 500mV.
Figure 49. Equivalent Internal ESD Circuitry and Its Relation to a Typical Circuit Application
An ESD event produces a short duration,
high-voltage pulse that is transformed into a short
duration, high-current pulse as it discharges through
a semiconductor device. The ESD protection circuits
are designed to provide a current path around the
operational amplifier core to prevent it from being
damaged. The energy absorbed by the protection
circuitry is then dissipated as heat.
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 illustrated in Figure 49, 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.
Figure 49 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 datasheet
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 0V.
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
18
Submit Documentation Feedback
Copyright © 2006–2009, Texas Instruments Incorporated
Product Folder Link(s): OPA211 OPA2211