OPA192 Datasheet, PDF (22/35 Pages) Texas Instruments – High Voltage, Rail-to-Rail Input/Output, Precision Operational Amplifiers, e-trim Series

OPA192
OPA2192
OPA4192
SBOS620A – DECEMBER 2013 – REVISED JANUARY 2014
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For additional drive capability in unity-gain configurations, capacitive load drive can be improved by inserting a
small (10 Ω to 20 Ω) resistor, R_ISO, in series with the output, as shown in Figure 52. 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 OPA192 well suited for applications such as reference
buffers, MOSFET gate drives, and cable-shield drives. The circuit shown in Figure 52 uses an isolation resistor
(R_ISO) to stabilize the output of an op amp. R_ISO modifies the open-loop gain of the system for increased phase
margin, and results using the OPA192 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 52. Extending Capacitive Load Drive with the OPA192
Table 3. OPA192 Capacitive Load Drive Solution Using Isolation Resistor Comparison of Calculated and
Measured Results
Capacitive Load
Phase Margin
R_ISO (Ω)
Measured
Overshoot (%)
Calculated PM
100 pF
45°
60°
47.0
360.0
23.2 8.6
10.4
45.1°
58.1°
1000 pF
45°
60°
24.0
100.0
22.5
9.0
45.8°
59.7°
0.01 µF
45°
60°
20.0
51.0
22.1
8.7
46.1°
60.1°
0.1 µF
45°
60°
6.2
15.8
23.1
8.6
45.2°
60.2°
1 µF
45°
60°
2.0
4.7
21.0
8.6
47.2°
60.2°
For step-by-step design procedure, circuit schematics, bill of materials, PCB files, simulation results, and test
results, refer to TI Precision Design TIDU032 - Capacitive Load Drive Solution using an Isolation Resistor
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