OPA1641 Datasheet, PDF (14/31 Pages) Texas Instruments – High-Performance, JFET-Input AUDIO OPERATIONAL AMPLIFIERS

OPA1641, OPA1642, OPA1644
SBOS484C – DECEMBER 2009 – REVISED DECEMBER 2015
Feature Description (continued)
www.ti.com
Output
+18V
OPA1641
-18V
37VPP
Sine Wave
(±18.5V)
Output
Time (0.4ms/div)
Figure 29. Output Waveform Devoid of Phase Reversal During an Input Overdrive Condition
7.3.2 Output Current Limit
The output current of the OPA164x series is limited by internal circuitry to 36 mA/–30 mA (sourcing and sinking),
to protect the device if the output is accidentally shorted. This short circuit current depends on temperature, as
shown in Figure 26.
Although it is uncommon for most modern audio applications to require 600-Ω load drive capability, many audio
operational amplifier applications continue to specify the total harmonic distortion (THD+N) at 600-Ω load for
comparative purposes. Figure 7 and Figure 8 provide typical THD+N measurement curves for the OPA164x
series, where the output drives a 3-V_RMS signal into a 600-Ω load. However, correct device operation cannot be
ensured when driving 600-Ω loads at full supply. Depending on supply voltage and temperature, it may well
trigger the output current limit circuitry of the device.
7.3.3 EMI Rejection Ratio (EMIRR)
The electromagnetic interference (EMI) rejection ratio, or EMIRR, describes the EMI immunity of operational
amplifiers. An adverse effect that is common to many operational amplifiers is a change in the offset voltage as a
result of RF signal rectification. An operational amplifier that is more efficient at rejecting this change in offset as
a result of EMI has a higher EMIRR and is quantified by a decibel value. Measuring EMIRR can be performed in
many ways, but this report provides the EMIRR IN+, which specifically describes the EMIRR performance when
the RF signal is applied to the noninverting input pin of the operational amplifier. In general, only the noninverting
input is tested for EMIRR for the following three reasons:
• Operational amplifier input pins are known to be the most sensitive to EMI, and typically rectify RF signals
better than the supply or output pins.
• The noninverting and inverting operational amplifier inputs have symmetrical physical layouts and exhibit
nearly matching EMIRR performance.
• EMIRR is easier to measure on noninverting pins than on other pins because the noninverting input terminal
can be isolated on a printed-circuit-board (PCB). This isolation allows the RF signal to be applied directly to
the noninverting input terminal with no complex interactions from other components or connecting PCB
traces.
A more formal discussion of the EMIRR IN+ definition and test method is provided in application report EMI
Rejection Ratio of Operational Amplifiers (SBOA128), available for download at www.ti.com.
The EMIRR IN+ of the OPA164x is plotted versus frequency as shown in Figure 30. If available, any dual and
quad operational amplifier device versions have nearly similar EMIRR IN+ performance. The OPA164x unity-gain
bandwidth is 11 MHz. EMIRR performance below this frequency denotes interfering signals that fall within the
operational amplifier bandwidth.
14
Submit Documentation Feedback
Copyright © 2009–2015, Texas Instruments Incorporated
Product Folder Links: OPA1641 OPA1642 OPA1644