OPA1688 Datasheet, PDF (20/41 Pages) Texas Instruments – OPA168x SoundPlus 36-V, Single-Supply, 10-MHz, Rail-to-Rail Output Operational Amplifiers

OPA1688, OPA1689
SBOS724 – SEPTEMBER 2015
www.ti.com
9.3.2 Phase-Reversal Protection
The OPA168x family has internal phase-reversal protection. Many op amps exhibit phase reversal when the
input is driven beyond the linear common-mode range. This condition is most often encountered in noninverting
circuits when the input is driven beyond the specified common-mode voltage range, causing the output to
reverse into the opposite rail. The input of the OPA168x prevents phase reversal with excessive common-mode
voltage. Instead, the appropriate rail limits the output voltage. This performance is shown in Figure 45.
V_OUT
V_IN
Time (200 s/div)
C011
Figure 45. No Phase Reversal
9.3.3 Capacitive Load and Stability
The dynamic characteristics of the OPA168x are optimized for commonly-used operating conditions. The
combination of low closed-loop gain and high capacitive loads decreases the phase margin of the amplifier and
may lead to gain peaking or oscillations. As a result, heavier capacitive loads must be isolated from the output.
The simplest way to achieve this isolation is to add a small resistor (for example, R_OUT = 50 Ω) in series with the
output. Figure 46 and Figure 47 show graphs of small-signal overshoot versus capacitive load for several values
of R_OUT; see application bulletin SBOA015 (AB-028), Feedback Plots Define Op Amp AC Performance, available
for download from www.ti.com, for details of analysis techniques and application circuits.
60
50
40
30
20
10
0
0
R_OUT = 0
RRO_OU=_T 2=525
RRO_OU=_T 5=050
100
200
300
400
500
Capacitive Load (pF)
C013
G = –1
Figure 46. Small-Signal Overshoot vs Capacitive Load
(100-mV Output Step)
50
40
30
20
10
0
0
R_OUT= 0
RRO_OU=_T=2255
RRO_OU=_T=5500
100
200
300
400
500
Capacitive Load (pF)
C013
G=1
Figure 47. Small-Signal Overshoot vs Capacitive Load
(100-mV Output Step)
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