SBOS557E August   2011  – April 2018 OPA170 , OPA2170 , OPA4170

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Smallest Packaging for 36-V Operational Amplifiers
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions: OPA170
    2.     Pin Functions: OPA2170
    3.     Pin Functions: OPA4170
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information: OPA170
    5. 7.5 Thermal Information: OPA2170
    6. 7.6 Thermal Information: OPA4170
    7. 7.7 Electrical Characteristics
    8. 7.8 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Operating Characteristics
      2. 8.3.2 Phase-Reversal Protection
      3. 8.3.3 Electrical Overstress
      4. 8.3.4 Capacitive Load and Stability
    4. 8.4 Device Functional Modes
      1. 8.4.1 Common-Mode Voltage Range
      2. 8.4.2 Overload Recovery
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Custom Design With WEBENCH® Tools
        2. 9.2.2.2 Unity-Gain Buffer
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
      2. 12.1.2 Development Support
        1. 12.1.2.1 TINA-TI™ (Free Software Download)
        2. 12.1.2.2 DIP Adapter EVM
        3. 12.1.2.3 Universal Operational Amplifier EVM
        4. 12.1.2.4 TI Precision Designs
        5. 12.1.2.5 WEBENCH Filter Designer
        6. 12.1.2.6 Custom Design With WEBENCH® Tools
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Related Links
    4. 12.4 Receiving Notification of Documentation Updates
    5. 12.5 Community Resources
    6. 12.6 Trademarks
    7. 12.7 Electrostatic Discharge Caution
    8. 12.8 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2.2 Unity-Gain Buffer

Figure 41 shows a unity-gain buffer driving a capacitive load. Equation 1 shows the transfer function for the circuit in Figure 41. Not shown in Figure 41 is the open-loop output resistance of the operational amplifier, Ro.

Equation 1. OPA170 OPA2170 OPA4170 ai_refdes_eqn_bos618.gif

The transfer function in Equation 1 has a pole and a zero. The frequency of the pole (fp) is determined by (Ro + RISO) and CLOAD. Components RISO and CLOAD determine the frequency of the zero (fz). A stable system is obtained by selecting RISO such that the rate of closure (ROC) between the open-loop gain (AOL) and 1/β is 20 dB/decade. Figure 42 depicts the concept. The 1/β curve for a unity-gain buffer is 0 dB.

OPA170 OPA2170 OPA4170 ai_refdes_bodeplot_bos618.gifFigure 42. Unity-Gain Amplifier With RISO Compensation

ROC stability analysis is typically simulated. The validity of the analysis depends on multiple factors, especially the accurate modeling of Ro. In addition to simulating the ROC, a robust stability analysis includes a measurement of overshoot percentage and ac gain peaking of the circuit using a function generator, oscilloscope, and gain and phase analyzer. Phase margin is then calculated from these measurements. Table 3 shows the overshoot percentage and ac gain peaking that correspond to phase margins of 45° and 60°. For more details on this design and other alternative devices that can be used in place of the OPA170, see the Precision Design, Capacitive Load Drive Solution Using an Isolation Resistor.

Table 3. Phase Margin versus Overshoot and AC Gain Peaking

PHASE MARGIN OVERSHOOT AC GAIN PEAKING
45° 23.3% 2.35 dB
60° 8.8% 0.28 dB