SBOS915 December   2017 TLV2172-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information: TLV2172-Q1
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Operating Characteristics
      2. 7.3.2 Phase-Reversal Protection
      3. 7.3.3 Electrical Overstress
      4. 7.3.4 Capacitive Load and Stability
    4. 7.4 Device Functional Modes
      1. 7.4.1 Common-Mode Voltage Range
      2. 7.4.2 Overload Recovery
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
        1. 11.1.2.1 TINA-TI™ (Free Software Download)
        2. 11.1.2.2 DIP Adapter EVM
        3. 11.1.2.3 Universal Op Amp EVM
        4. 11.1.2.4 TI Precision Designs
        5. 11.1.2.5 WEBENCH Filter Designer
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Related Links
    4. 11.4 Receiving Notification of Documentation Updates
    5. 11.5 Community Resources
    6. 11.6 Trademarks
    7. 11.7 Electrostatic Discharge Caution
    8. 11.8 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The TLV2172-Q1 operational amplifier provides high overall performance in a large number of general-purpose applications. As with all amplifiers, applications with noisy or high-impedance power supplies require decoupling capacitors placed close to the device pins. In most cases, 0.1-µF capacitors are adequate. Follow the additional recommendations in the Layout Guidelines section to achieve the maximum performance from this device. Many applications introduce capacitive loading to the output of the amplifier (which potentially causes instability). To stabilize the amplifier, add an isolation resistor between the amplifier output and the capacitive load. Typical Application section shows the process for selecting a resistor.

8.2 Typical Application

This circuit can drive capacitive loads (such as cable shields, reference buffers, MOSFET gates, and diodes). The circuit uses an isolation resistor (RISO) to stabilize the output of an operational amplifier. RISO modifies the open-loop gain of the system to ensure that the circuit has sufficient phase margin.

TLV2172-Q1 refdes_blocldia_sbos782.gif Figure 29. Unity-Gain Buffer With RISO Stability Compensation

8.2.1 Design Requirements

The design requirements are:

  • Supply voltage: 30 V (±15 V)
  • Capacitive loads: 100 pF, 1000 pF, 0.01 μF, 0.1 μF, and 1 μF
  • Phase margin: 45° and 60°

8.2.2 Detailed Design Procedure

Figure 29 shows a unity-gain buffer driving a capacitive load. Equation 1 shows the transfer function for the circuit in Figure 29.Figure 29 does not show the open-loop output resistance of the operational amplifier (Ro).

Equation 1. TLV2172-Q1 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. The RISO and CLOAD components determine the frequency of the zero (fz). A stable system is obtained by selecting RISO so that the rate of closure (ROC) between the open-loop gain (AOL) and 1/β is 20 dB per decade. Figure 30 shows the concept. The 1/β curve for a unity-gain buffer is 0 dB.

TLV2172-Q1 ai_refdes_bodeplot_bos618.gif Figure 30. Unity-Gain Amplifier With RISO Compensation

Typically, ROC stability analysis is 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 replace the TLV2172-Q1, see the Capacitive Load Drive Solution Using an Isolation Resistor precision design.

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

8.2.3 Application Curve

The values of RISO that yield phase margins of 45º and 60º for various capacitive loads are determined using the described methodology. Figure 31 shows the results.

TLV2172-Q1 C042_SBOS618.png Figure 31. Isolation Resistor Required for Various Capacitive Loads to Achieve a Target Phase Margin