SBOA602 November   2024 OPA593

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Current Booster, Push-Pull Topology Output Characteristics
    1. 2.1 Open-Loop Output Impedance
    2. 2.2 Minimizing Zero Crossover Distortion
  6. 3Various Current Booster Configurations
    1. 3.1 Complementary MOSFET versus BJT Current Booster Comparisons
  7. 4Stabilizing a Design for Power Amplifier Driving 1μF Capacitive Load (CL)
    1. 4.1 Op-Amp Driving Resistive Load
    2. 4.2 Op-Amp Driving Capacitive Load and Challenges
    3. 4.3 Open-Loop AC Stability Analysis - Compensating CL Effects Using DFC
    4. 4.4 Closed-Loop Stability Response - Small Signal Step Transient Analysis
    5. 4.5 Effects of Riso on Frequency Response in Dual Feedback Compensation
    6. 4.6 Summary of the DFC Technique
  8. 5Stabilizing the OPA593 and Darlington Current Booster for 1μF Capacitive Load
    1. 5.1 Open-Loop AC Stability Analysis - Composite Op-Amp Driving 1μF CL
    2. 5.2 Closed-Loop Stability Response - Composite Op-Amp's Step Transient Analysis
  9. 6Composite Amplifier's Effective BW and Step Time Response
  10. 7Test Bench Validation
  11. 8Summary
  12. 9References

4 Stabilizing a Design for Power Amplifier Driving 1μF Capacitive Load (CL)

To effectively understand dual feedback compensation (DFC) techniques and make sure of loop stability, recognize the interactions between resistive and capacitive loads, as well as the open-loop output impedance of the power amplifier. Proper management of the placement of poles and zeros within a feedback system is vital for achieving stability and performance.

Using a power amplifier (PA) Spice model, such as the one provided by the Tina simulator, can streamline the analysis and enhance comprehension of the DFC approach. This model mimics the performance characteristics of the OPA593 with the current booster composite amplifier, offering a clear framework for understanding the DFC technique. The emulated Spice model emphasizes the key interactions among compensated components, including the output resistive load (RL), capacitive load (CL), feedback resistors (RF, RI), and the op-amp's open-loop output impedance (Zo), as shown in Figure 4-1.

Table 4-1summarizes the op-amp behaviors of the emulated Spice model for the OPA593 + current booster composite amplifier. Table 4-2 outlines the design requirements for the power amplifier, which is intended to drive 1μF capacitive and resistive loads with an output current rated up to ±1Adc.

Emulated Power Amp Drives a Resistive Load - Open-Loop AC Stability Analysis Figure 4-1 Emulated Power Amp Drives a Resistive Load - Open-Loop AC Stability Analysis
Table 4-1 Key Parameters of the Emulated Power Amplifier
Design Parameters Modified PA Specification
Open-loop gain 1 × 106V/V or 120dB
Dominated pole 10Hz
Open-loop output impedance 1Ω
Maximum output current 2A
Power amplifier's second poles 50MHz