SBOS875B August   2017  – July 2018 THS3491


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Typical Arbitrary Waveform Generator Output Drive Circuit
      2.      Harmonic Distortion vs Frequency
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1.     Pin Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics: VS = ±15 V
    6. 7.6 Electrical Characteristics: VS = ±7.5 V
    7. 7.7 Typical Characteristics: ±15 V
    8. 7.8 Typical Characteristics: ±7.5 V
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Power-Down (PD) Pin
      2. 8.3.2 Power-Down Reference (REF) Pin
      3. 8.3.3 Internal Junction Temperature Sense (TJ_SENSE) Pin
    4. 8.4 Device Functional Modes
      1. 8.4.1 Wideband Noninverting Operation
      2. 8.4.2 Wideband, Inverting Operation
      3. 8.4.3 Single-Supply Operation
      4. 8.4.4 Maximum Recommended Output Voltage
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Driving Capacitive Loads
      2. 9.1.2 Video Distribution
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 PowerPAD™ Integrated Circuit Package Design Considerations (DDA Package Only)
        1. PowerPAD™ Integrated Circuit Package Layout Considerations
        2. Power Dissipation and Thermal Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Power Dissipation and Thermal Considerations

The THS3491 includes automatic thermal shutoff protection. This protection circuitry shuts down the amplifier if the junction temperature exceeds approximately 160°C. When the junction temperature decreases to approximately 145°C, the amplifier turns on again. However, for maximum performance and reliability, make sure that the design does not exceed a junction temperature of 125°C. Between 125°C and 150°C, damage does not occur, but the performance of the amplifier begins to degrade and long-term reliability suffers. The package and the PCB dictate the thermal characteristics of the device. Maximum power dissipation for a particular package is calculated using the following formula.

Equation 1. THS3491 ths3491-pdmax-equation.gif


  • PDmax is the maximum power dissipation in the amplifier (W).
  • Tmax is the absolute maximum junction temperature (°C).
  • TA is the ambient temperature (°C).
  • θJA = θJC + θCA
  • θJC is the thermal coefficient from the silicon junctions to the case (°C/W).
  • θCA is the thermal coefficient from the case to ambient air (°C/W).

The thermal coefficient for the PowerPAD integrated circuit packages are substantially improved over the traditional SOIC package. The data for the PowerPAD packages assume a board layout that follows the PowerPAD package layout guidelines referenced above and detailed in PowerPAD™ Thermally Enhanced Package. Maximum power dissipation levels are shown in Comparison of θJA for Various Packages. If the PowerPAD integrated circuit package is not soldered to the PCB, the thermal impedance increases substantially and may cause serious heat and performance issues. Take care to always solder the PowerPAD integrated circuit package to the PCB for optimum performance.

When determining whether or not the device satisfies the maximum power dissipation requirement, make sure to consider not only quiescent power dissipation, but dynamic power dissipation. Often times, this dissipation is difficult to quantify because the signal pattern is inconsistent, but an estimate of the RMS power dissipation provides visibility into a possible problem.