OPA2172 Datasheet, PDF (20/42 Pages) Texas Instruments – OPAx172 36-V, Single-Supply, 10-MHz, Rail-to-Rail Output Operational Amplifiers

OPA172, OPA2172, OPA4172
SBOS618H – DECEMBER 2013 – REVISED SEPTEMBER 2015
www.ti.com
8.3.2 Phase-Reversal Protection
The OPAx172 family has internal phase-reversal protection. Many op amps exhibit a 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 OPAx172 prevents phase reversal with excessive common-mode
voltage. Instead, the appropriate rail limits the output voltage. This performance is shown in Figure 43.
+ 18 V
±
OPA172
+
+
± 37 VPP ± 18 V
Sine Wave
(±18.5V)
VOUT
V_OUT
V_IN
Time (200 s/div)
C011
Figure 43. No Phase Reversal
8.3.3 Capacitive Load and Stability
The dynamic characteristics of the OPAx172 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 44 and Figure 45 show graphs of small-signal overshoot versus capacitive load for several values
of R_OUT. Refer to 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
RI = 1 k
50
+
VIN = 100mV
±
40
RF = 1 k
+ 18 V
±
OPA172
+
± 18 V
ROUT
CL
G = -1
30
20
R_OUT = 0
10
RR_OO_UT==2255
0
0p
100p
200p
300p
RR_OO_UT==5500
400p
500p
Capacitive Load (F)
C013
Figure 44. Small-Signal Overshoot vs Capacitive Load
(100-mV Output Step)
50
G = +1
40
30
20
10
0
0p
100p
R_OUT= 0
RO = 25 R = 25 _OUT
+
VIN = 100mV
±
RR_OO_UT==5500
200p
300p
+ 18 V
±
OPA172
+
± 18 V
ROUT
RL
CL
400p
500p
Capacitive Load (F)
C013
Figure 45. Small-Signal Overshoot vs Capacitive Load
(100-mV Output Step)
20
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