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

3.1 Complementary MOSFET versus BJT Current Booster Comparisons

Table 3-1 compares the pros and cons of CMOSFET and CBJT current drivers, which are two of the most popular and cost-effective options. Although detailed comparisons are not provided in this section, note that there are significant differences and trade-offs that need to be considered when selecting current boosters for a specific application.

Table 3-1 Pros and Cons Comparisons Between CMOSFET and CBJT in Current Booster Applications
No.Complementary MOSFET (CMOSFET) Output StageComplementary BJT (CBJT) Output Stage
1Faster switching on and off speeds, possible in MHz, wider BWSlower switching speeds, possible in the 100s kHz range, lower BW
2High input impedance, lower standby power dissipationLow input impedance, higher standby power dissipation
3Slightly higher intrinsic output impedance, if normalized in theoryLower intrinsic output impedance in theory
4VDS interface exhibits PTC over temperatureICE interface exhibits NTC over temperature
5Less prone to classical second breakdown, requires device protectionsComparable to MOSFET devices, require device protections
6Lower transconductance, gm- Lower voltage gain per stageHigher transconductance, gm- higher voltage gain per stage
7Better power dissipation, better thermal stability and performance, simpler thermal managementHigher power dissipation, prone to thermal runaway, requires more thermal management circuitry
8Requires a higher VGS threshold voltage to turn onLower VBE voltage, requires approximately 0.65V forward biased voltage to turn on
9As VGS increases, the conductivity of drain-source increasesAs IBE increases, the conductivity of collector-emitter increases
10Designed for wider voltage and high current power applicationsDesigned for high current gain applications
11Operates in the triode or linear region; voltage-controlled current-sourceOperates in the active region; current-controlled current-source
12Slightly higher costs than BJT devicesGenerally lower costs than MOSFET devices
13pA to nA DC input bias current at the gateµA to mA DC input bias current at the base
14Lower current density per unit areaHigher current density per unit area
15Better for high power linear regulator, and higher headroomBetter linearity, simpler to control, and lower headroom