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OPA445ADDAR Datasheet(PDF) 9 Page - Texas Instruments |
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OPA445ADDAR Datasheet(HTML) 9 Page - Texas Instruments |
9 / 25 page OPA445 SBOS156B − MARCH 1987 − REVISED APRIL 2008 www.ti.com 9 CAPACITIVE LOADS The dynamic characteristics of the OPA445 have been optimized for commonly encountered gains, loads, and operating conditions. The combination of low closed-loop gain and capacitive load will decrease the phase margin and may lead to gain peaking or oscillations. Figure 3 shows a circuit which preserves phase margin with capacitive load. The circuit does not suffer a voltage drop due to load current; however, input impedance is reduced at high frequencies. Consult Application Bulletin SBOA015, available for download at www.ti.com, for details of analysis techniques and application circuits. V O C L 5000pF R 2 R 1 G= 1 + R 2 2k Ω R 1 2k Ω V IN NOTE: Design equations and component values are approximate. User adjustment is required for optimum performance. R C 20 Ω C C 0.22 µF R C = R 2 2C L × 10 10 − (1 + R 2/R1) OPA445 C C = C L × 10 3 R C Figure 3. Driving Large Capacitive Loads INCREASING OUTPUT CURRENT In those applications where the 15mA of output current is not sufficient to drive the required load, output current can be increased by connecting two or more OPA445s in parallel as shown in Figure 4. Amplifier A1 is the master amplifier and may be configured in virtually any op amp circuit. Amplifier A2, the slave, is configured as a unity gain buffer. Alternatively, external output transistors can be used to boost output current. The circuit in Figure 5 is capable of supplying output currents up to 1A. R 1 R 2 OPA445 OPA445 Slave Master V IN R S (1) 10 Ω R S (1) 10 Ω R L NOTE: (1) R S resistors minimize the circulating current that will always flow between the two devices due to V OS errors. Figure 4. Parallel Amplifiers Increase Output Current Capability R 1 R 2 OPA445 TIP30C TIP29C V IN +45V −45V V O R 3 (1) 100 Ω NOTE: (1) Provides current limit for OPA445 and allows the amplifier to drive the load when the output is between +0.7V and −0.7V. R 4 0.2 Ω R 4 0.2 Ω LOAD C F Figure 5. External Output Transistors Boost Output Current Up to 1 Amp |
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