Datasheet

OPA1641
OPA1642
OPA1644
SBOS484B –DECEMBER 2009–REVISED AUGUST 2010 www.ti.com
Although the output current is limited by internal An ESD event produces a short duration,
protection circuitry, accidental shorting of one or more high-voltage pulse that is transformed into a short
output channels of a device can result in excessive duration, high-current pulse as it discharges through
heating. For instance, when an output is shorted to a semiconductor device. The ESD protection circuits
mid-supply, the typical short-circuit current of 36mA are designed to provide a current path around the
leads to an internal power dissipation of over 600mW operational amplifier core to prevent it from being
at a supply of ±18V. In case of a dual OPA1642 in an damaged. The energy absorbed by the protection
MSOP-8 package (thermal resistance q
JA
= circuitry is then dissipated as heat.
180°C/W), such a power dissipation would lead the
When an ESD voltage develops across two or more
die temperature to be 220°C above ambient
of the amplifier device pins, current flows through one
temperature, when both channels are shorted. This
or more of the steering diodes. Depending on the
temperature increase would destroy the device.
path that the current takes, the absorption device
In order to prevent such excessive heating that can may activate. The absorption device has a trigger, or
destroy the device, the OPA164x series has an threshold voltage, that is above the normal operating
internal thermal shutdown circuit, which shuts down voltage of the OPA164x but below the device
the device if the die temperature exceeds breakdown voltage level. Once this threshold is
approximately +180°C. Once this thermal shutdown exceeded, the absorption device quickly activates
circuit activates, a built-in hysteresis of 15°C ensures and clamps the voltage across the supply rails to a
that the die temperature must drop to about +165°C safe level.
before the device switches on again.
When the operational amplifier connects into a circuit
such as the one Figure 35 shows, the ESD protection
ELECTRICAL OVERSTRESS
components are intended to remain inactive and not
become involved in the application circuit operation.
Designers often ask questions about the capability of
However, circumstances may arise where an applied
an operational amplifier to withstand electrical
voltage exceeds the operating voltage range of a
overstress. These questions tend to focus on the
given pin. Should this condition occur, there is a risk
device inputs, but may involve the supply voltage pins
that some of the internal ESD protection circuits may
or even the output pin. Each of these different pin
be biased on, and conduct current. Any such current
functions have electrical stress limits determined by
flow occurs through steering diode paths and rarely
the voltage breakdown characteristics of the
involves the absorption device.
particular semiconductor fabrication process and
specific circuits connected to the pin. Additionally,
Figure 35 depicts a specific example where the input
internal electrostatic discharge (ESD) protection is
voltage, V
IN
, exceeds the positive supply voltage
built into these circuits to protect them from
(+V
S
) by 500mV or more. Much of what happens in
accidental ESD events both before and during
the circuit depends on the supply characteristics. If
product assembly.
+V
S
can sink the current, one of the upper input
steering diodes conducts and directs current to +V
S
.
It is helpful to have a good understanding of this
Excessively high current levels can flow with
basic ESD circuitry and its relevance to an electrical
increasingly higher V
IN
. As a result, the datasheet
overstress event. Figure 35 illustrates the ESD
specifications recommend that applications limit the
circuits contained in the OPA164x series (indicated
input current to 10mA.
by the dashed line area). The ESD protection circuitry
involves several current-steering diodes connected
If the supply is not capable of sinking the current, V
IN
from the input and output pins and routed back to the
may begin sourcing current to the operational
internal power-supply lines, where they meet at an
amplifier, and then take over as the source of positive
absorption device internal to the operational amplifier.
supply voltage. The danger in this case is that the
This protection circuitry is intended to remain inactive
voltage can rise to levels that exceed the operational
during normal circuit operation.
amplifier absolute maximum ratings.
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