OPA211-EP_15 Datasheet, PDF (20/26 Pages) Texas Instruments – 1.1nV/√Hz NOISE, LOW POWER, PRECISION OPERATIONAL AMPLIFIER

OPA211-EP
SBOS638 – JUNE 2012
Figure 50 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
www.ti.com
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
most likely will not operate normally. If the supplies
are low impedance, then the current through the
steering diodes can become quite high. The current
level depends on the ability of the input source to
deliver current, and any resistance in the input path.
8.8 THERMAL CONSIDERATIONS
The primary issue with all semiconductor devices is
junction temperature (T_J). The most obvious
consideration is assuring that T_J never exceeds the
absolute maximum rating specified for the device.
However, addressing device thermal dissipation has
benefits beyond protecting the device from damage.
Even modest increases in junction temperature can
decrease op amp performance, and temperature-
related errors can accumulate. Understanding the
power generated by the device within the specific
application and assessing the thermal effects on the
error tolerance lead to a better understanding of
system performance and thermal dissipation needs.
20
Submit Documentation Feedback
Product Folder Links: OPA211-EP
Copyright © 2012, Texas Instruments Incorporated