Datasheet

OPA1662
OPA1664
www.ti.com SBOS489 –DECEMBER 2011
POWER DISSIPATION When the operational amplifier connects into a circuit
such as that illustrated in Figure 48, the ESD
The OPA1662 and OPA1664 series op amps are
protection components are intended to remain
capable of driving 2-kΩ loads with a power-supply
inactive and not become involved in the application
voltage up to ±18 V and full operating temperature
circuit operation. However, circumstances may arise
range. Internal power dissipation increases when
where an applied voltage exceeds the operating
operating at high supply voltages. Copper leadframe
voltage range of a given pin. Should this condition
construction used in the OPA166x series op amps
occur, there is a risk that some of the internal ESD
improves heat dissipation compared to conventional
protection circuits may be biased on, and conduct
materials. Circuit board layout can also help minimize
current. Any such current flow occurs through
junction temperature rise. Wide copper traces help
steering diode paths and rarely involves the
dissipate the heat by acting as an additional heat
absorption device.
sink. Temperature rise can be further minimized by
soldering the devices to the circuit board rather than Figure 48 depicts a specific example where the input
using a socket. 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
ELECTRICAL OVERSTRESS
+V
S
can sink the current, one of the upper input
Designers often ask questions about the capability of
steering diodes conducts and directs current to +V
S
.
an operational amplifier to withstand electrical
Excessively high current levels can flow with
overstress. These questions tend to focus on the
increasingly higher V
IN
. As a result, the datasheet
device inputs, but may involve the supply voltage pins
specifications recommend that applications limit the
or even the output pin. Each of these different pin
input current to 10 mA.
functions have electrical stress limits determined by
If the supply is not capable of sinking the current, V
IN
the voltage breakdown characteristics of the
may begin sourcing current to the operational
particular semiconductor fabrication process and
amplifier, and then take over as the source of positive
specific circuits connected to the pin. Additionally,
supply voltage. The danger in this case is that the
internal electrostatic discharge (ESD) protection is
voltage can rise to levels that exceed the operational
built into these circuits to protect them from
amplifier absolute maximum ratings. In extreme but
accidental ESD events both before and during
rare cases, the absorption device triggers on while
product assembly.
+V
S
and –V
S
are applied. If this event happens, a
It is helpful to have a good understanding of this
direct current path is established between the +V
S
basic ESD circuitry and its relevance to an electrical
and –V
S
supplies. The power dissipation of the
overstress event. Figure 48 illustrates the ESD
absorption device is quickly exceeded, and the
circuits contained in the OPA166x (indicated by the
extreme internal heating destroys the operational
dashed line area). The ESD protection circuitry
amplifier.
involves several current-steering diodes connected
Another common question involves what happens to
from the input and output pins and routed back to the
the amplifier if an input signal is applied to the input
internal power-supply lines, where they meet at an
while the power supplies +V
S
and/or –V
S
are at 0 V.
absorption device internal to the operational amplifier.
Again, it depends on the supply characteristic while at
This protection circuitry is intended to remain inactive
0 V, or at a level below the input signal amplitude. If
during normal circuit operation.
the supplies appear as high impedance, then the
An ESD event produces a short duration,
operational amplifier supply current may be supplied
high-voltage pulse that is transformed into a short
by the input source via the current steering diodes.
duration, high-current pulse as it discharges through
This state is not a normal bias condition; the amplifier
a semiconductor device. The ESD protection circuits
most likely will not operate normally. If the supplies
are designed to provide a current path around the
are low impedance, then the current through the
operational amplifier core to prevent it from being
steering diodes can become quite high. The current
damaged. The energy absorbed by the protection
level depends on the ability of the input source to
circuitry is then dissipated as heat.
deliver current, and any resistance in the input path.
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 internal to the
OPA166x triggers when a fast ESD voltage pulse is
impressed across the supply pins. Once triggered, it
quickly activates, clamping the ESD pulse to a safe
voltage level.
Copyright © 2011, Texas Instruments Incorporated 17
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