OPA191_017 Datasheet, PDF (27/51 Pages) Texas Instruments – 36-V, Low Power, Precision, CMOS, Rail-to-Rail Input/Output, Low Offset Voltage, Low Input Bias Current Op Amp

www.ti.com
OPA191, OPA2191, OPA4191
SBOS701A – DECEMEBER 2015 – REVISED APRIL 2016
For additional drive capability in unity-gain configurations, improve capacitive load drive by inserting a small,
10-Ω to 20-Ω resistor (R_ISO) in series with the output, as shown in Figure 57. This resistor significantly reduces
ringing while maintaining dc performance for purely capacitive loads. However, if there is a resistive load in
parallel with the capacitive load, a voltage divider is created, introducing a gain error at the output and slightly
reducing the output swing. The error introduced is proportional to the ratio R_ISO / R_L, and is generally negligible at
low output levels. A high capacitive load drive makes the OPA191 well suited for applications such as reference
buffers, MOSFET gate drives, and cable-shield drives. The circuit shown in Figure 57 uses R_ISO to stabilize the
output of an op amp. R_ISO modifies the open-loop gain of the system for increased phase margin. Results using
the OPA191 are summarized in Table 3. For additional information on techniques to optimize and design using
this circuit, TI Precision Design TIDU032 details complete design goals, simulation, and test results.
+V_s
R_iso
V_out
+
V_{in ±}
-V_s
C_load
Figure 57. Extending Capacitive Load Drive With the OPA191
Table 3. OPA191 Capacitive Load Drive Solution Using Isolation Resistor Comparison of Calculated and
Measured Results
PARAMETER
Capacitive Load
Phase Margin
R_ISO (Ω)
Measured
Overshoot (%)
100 pF
45°
280
23
1000 pF
45°
60°
113
432
23
8
VALUE
0.01 µF
45°
60°
68
210
23
8
0.1 µF
45°
60°
17.8
53.6
23
8
1 µF
45°
60°
3.6
10
23
8
For step-by-step design procedure, circuit schematics, bill of materials, printed circuit board (PCB) files,
simulation results, and test results, refer to TI Precision Design TIDU032, Capacitive Load Drive Solution using
an Isolation Resistor .
Copyright © 2015–2016, Texas Instruments Incorporated
Submit Documentation Feedback
27
Product Folder Links: OPA191 OPA2191 OPA4191