SLOS432B April   2004  – October 2015 THS4281

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
    5. 6.5 Electrical Characteristics, VS = 3 V (VS+ = 3 V, VS- = GND)
    6. 6.6 Electrical Characteristics, VS = 5 V (VS+ = 5 V, VS- = GND)
    7. 6.7 Electrical Characteristics, VS = ±5 V
    8. 6.8 Dissipation Ratings
    9. 6.9 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
      1. 7.1.1 High-Speed Operational Amplifiers
    2. 7.2 Feature Description
      1. 7.2.1 Wideband, Noninverting Operation
      2. 7.2.2 Wideband, Inverting Operation
    3. 7.3 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Single-Supply Operation
      2. 8.1.2 Driving Capacitive Loads
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Active Filtering With the THS4281
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
    1. 9.1 Power-Supply Decoupling Techniques and Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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発注情報

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

8.1.1 Single-Supply Operation

The THS4281 is designed to operate from a single 2.7-V to 16.5-V power supply. When operating from a single power supply, care must be taken to ensure the input signal and amplifier are biased appropriately to allow for the maximum output voltage swing and not violate VICR. The circuits shown in Figure 70 shows inverting and noninverting amplifiers configured for single-supply operation.

THS4281 dc_sso_los432.gif Figure 70. DC-Coupled Single Supply Operation

8.1.2 Driving Capacitive Loads

One of the most demanding, and yet common, load conditions for an op amp is capacitive loading. Often, the capacitive load is the input of an A/D converter, including additional external capacitance, which may be recommended to improve A/D linearity. A high-speed, high open-loop gain amplifier like the THS4281 can be susceptible to instability and peaking when a capacitive load is placed directly on the output. When the amplifier open-loop output resistance is considered, this capacitive load introduces an additional pole in the feedback path that decreases the phase margin. When the primary considerations are frequency response flatness, pulse response fidelity, or distortion, a simple and effective solution is to isolate the capacitive load from the feedback loop by inserting a small series isolation resistor (for example, R(ISO) = 100 Ω for CLOAD = 10 pF to R(ISO) = 10 Ω for CLOAD = 1000 pF) between the amplifier output and the capacitive load.

8.2 Typical Application

THS4281 sk_cir_los432.gif
Figure 71. Second-Order Sallen-Key 100-kHz Butterworth Filter, Gain = 2 V/V
THS4281 mfb_cir_los432.gif Figure 72. Second-Order MFB 100-kHz Butterworth Filter, Gain = 2 V/V

8.2.1 Design Requirements

Table 1 shows example design parameters and values for the typical application design example in Figure 71.

Table 1. Design Parameters

DESIGN PARAMETERS VALUE
Supply voltage ±5 V
Amplifier topology Voltage feedback
Gain 2 V/V
Filter requirement Second Order 100 KHz Sallen- Key Butterworth Filter
Input/Output Requirements Rail to Rail

8.2.2 Detailed Design Procedure

8.2.2.1 Active Filtering With the THS4281

High-performance active filtering with the THS4281 is achievable due to the amplifier's good slew rate, wide bandwidth, and voltage-feedback architecture. Several options are available for high-pass, low-pass, bandpass, and bandstop filters of varying orders. Filters can be quite complex and time consuming to design. Several books and application reports are available to help design active filters. But, to help simplify the process and minimize the chance of miscalculations, Texas Instruments has developed a filter design program called FilterPro™. FilterPro is available for download at no cost from TI's web site (www.ti.com).

The two most common low-pass filter circuits used are the Sallen-Key filter and the Multiple Feedback (MFB) – aka Rauch filter. FilterPro was used to determine a 2-pole Butterworth response filter with a corner (–3-dB) frequency of 100 kHz, which is shown in Figure 71 and Figure 72. One of the advantages of the MFB filter, a much better high-frequency rejection, is clearly shown in the response shown in Figure 75. This is due to the inherent R-C filter to ground being the first elements in the design of the MFB filter. The Sallen-Key design also has an R-C filter, but the capacitor connects directly to the output. At very high frequencies, where the amplifier's access loop gain is decreasing, the ability of the amplifier to reject high frequencies is severely reduced and allows the high-frequency signals to pass through the system. One other advantage of the MFB filter is the reduced sensitivity in component variation. This is important when using real-world components where capacitors can easily have ±10% variations.

8.2.3 Application Curves

THS4281 ai_vo2_frq_los432.gif Figure 73. Signal Gain vs
Frequency, VS = 3 V
THS4281 tc_g2_f_los432.png Figure 75. Second-Order 100-kHz Active Filter Response
THS4281 ai_vo_frq_los432.gif Figure 74. Signal Gain vs
Frequency, VS = ±5 V