OPA172IDR Datasheet, PDF (16/29 Pages) Texas Instruments – 36-V Single-Supply 10-MHz Rail-to-Rail Output Operational Amplifiers

OPA172
OPA2172
OPA4172
SBOS618 – DECEMBER 2013
www.ti.com
CAPACITIVE LOAD AND STABILITY
The dynamic characteristics of the OPAx172 have been optimized for commonly-encountered operating
conditions. The combination of low closed-loop gain and high capacitive loads decreases the phase margin of
the amplifier and can 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 43 and Figure 44 illustrate graphs of small-signal overshoot versus capacitive
load for several values of R_OUT. Also, 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
10
0
0p
100p
200p
300p
Capacitive Load (F)
R_OUT = 0
RR_OO_UT==2255
RR_OO_UT==5500
400p
500p
C013
Figure 43. 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
Capacitive Load (F)
+ 18 V
±
OPA172
+
± 18 V
ROUT
RL
CL
400p
500p
C013
Figure 44. Small-Signal Overshoot vs Capacitive Load (100-mV Output Step)
16
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