SBOS867E August   2017  – August 2025 OPA838

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Related Products
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics VS = 5 V
    6. 6.6 Electrical Characteristics VS = 3 V
    7. 6.7 Typical Characteristics: VS = 5 V
    8. 6.8 Typical Characteristics: VS = 3 V
    9. 6.9 Typical Characteristics: Over Supply Range
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Input Common-Mode Voltage Range
      2. 7.3.2 Output Voltage Range
      3. 7.3.3 Power-Down Operation
      4. 7.3.4 Trade-Offs in Selecting The Feedback Resistor Value
      5. 7.3.5 Driving Capacitive Loads
    4. 7.4 Device Functional Modes
      1. 7.4.1 Split-Supply Operation (±1.35 V to ±2.7 V)
      2. 7.4.2 Single-Supply Operation (2.7 V to 5.4 V)
      3. 7.4.3 Power Shutdown Operation
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Noninverting Amplifier
      2. 8.1.2 Inverting Amplifier
      3. 8.1.3 Output DC Error Calculations
      4. 8.1.4 Output Noise Calculations
    2. 8.2 Typical Applications
      1. 8.2.1 High-Gain Differential I/O Designs
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Transimpedance Amplifier
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curve
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 TINA-TI™ Simulation Software (Free Download)
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

7.3.5 Driving Capacitive Loads

The OPA838 drives small capacitive loads directly without oscillation (less than 6pF). When driving capacitive loads greater than 6 pF, Figure 6-50 illustrates the recommended ROUT vs capacitor load parametric on gains. At higher gains, the amplifier starts with greater phase margin into a resistive load and is able to operate with lower ROUT for a given capacitive load. Without ROUT, output capacitance interacts with the output impedance of the amplifier, which causes phase shift in the loop gain of the amplifier that reduces the phase margin. This phase shift causes peaking in the frequency response with overshoot and ringing in the pulse response. Figure 6-50 targets a 30° phase margin for the OPA838. A 30° phase margin produces a 5.7‑dB peaking in the frequency response at the amplifier output pin that is rolled off by the output RC pole; see Figure 7-7. This peaking potentially causes clipping for large signals driving a capacitive load. Increasing the ROUT value helps reduce the peaking at the cost of a more band-limited overall response.

OPA838 ROUT versus CL Test Circuit Figure 7-6 ROUT versus CL Test Circuit
OPA838 Frequency Response to Output Pin and Capacitive Load Figure 7-7 Frequency Response to Output Pin and Capacitive Load