OPA211-EP Datasheet, PDF (18/23 Pages) Texas Instruments – 1.1nV/√Hz NOISE, LOW POWER, PRECISION OPERATIONAL AMPLIFIER

OPA211-EP
SBOS638 – JUNE 2012
ELECTRICAL OVERSTRESS
Designers often ask questions about the capability of
an operational amplifier to withstand electrical
overstress. These questions tend to focus on the
device inputs, but may involve the supply voltage pins
or even the output pin. Each of these different pin
functions have electrical stress limits determined by
the voltage breakdown characteristics of the
particular semiconductor fabrication process and
specific circuits connected to the pin. Additionally,
internal electrostatic discharge (ESD) protection is
built into these circuits to protect them from
accidental ESD events both before and during
product assembly.
It is helpful to have a good understanding of this
basic ESD circuitry and its relevance to an electrical
overstress event. Figure 50 illustrates the ESD
circuits contained in the OPA211 (indicated by the
dashed line area). The ESD protection circuitry
involves several current-steering diodes connected
from the input and output pins and routed back to the
internal power-supply lines, where they meet at an
absorption device internal to the operational amplifier.
This protection circuitry is intended to remain inactive
during normal circuit operation.
R_F
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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 50, 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_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 50. Equivalent Internal ESD Circuitry and Its Relation to a Typical Circuit Application
18
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