SBOS855E January   2017  – December 2022 OPA1677 , OPA1678 , OPA1679

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: OPA1677
    5. 6.5 Thermal Information: OPA1678
    6. 6.6 Thermal Information: OPA1679
    7. 6.7 Electrical Characteristics
    8. 6.8 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 Phase Reversal Protection
      2. 7.3.2 Electrical Overstress
      3. 7.3.3 EMI Rejection Ratio (EMIRR)
        1. 7.3.3.1 EMIRR IN+ Test Configuration
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operating Voltage
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Capacitive Loads
    2. 8.2 Typical Applications
      1. 8.2.1 Phantom-Powered Preamplifier for Piezo Contact Microphones
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Power Supply
          2. 8.2.1.2.2 Input Network
          3. 8.2.1.2.3 Gain
          4. 8.2.1.2.4 Output Network
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Phono Preamplifier for Moving Magnet Cartridges
      3. 8.2.3 Single-Supply Electret Microphone Preamplifier
      4. 8.2.4 Composite Headphone Amplifier
      5. 8.2.5 Differential Line Receiver With AC-Coupled Outputs
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Power Dissipation
      2. 8.4.2 Layout Example
  9. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 PSpice® for TI
        2. 9.1.1.2 TINA-TI™ Simulation Software (Free Download)
        3. 9.1.1.3 DIP-Adapter-EVM
        4. 9.1.1.4 DIYAMP-EVM
        5. 9.1.1.5 TI Reference Designs
        6. 9.1.1.6 Filter Design Tool
    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
  10. 10Mechanical, Packaging, and Orderable Information

Package Options

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

R7, R8, and R9 determines the gain of the preamplifier circuit. The gain of the circuit is shown in Equation 6:

Equation 6. GUID-6B94435D-D9C1-4273-861D-2BDACF1DDFFA-low.gif

Resistors R7 and R9 are selected with a value of 2 kΩ to avoid loading the output of the OPA1678 and producing distortion. The value of R8 is then calculated in Equation 7:

Equation 7. GUID-7E9CB408-99AE-464F-B5D7-689DC4D4E7EE-low.gif

Capacitors C3 and C4 limit the bandwidth of the circuit so that signals outside the audio bandwidth are not amplified. The corner frequency produced by capacitors C3 and C4 is shown in Equation 8. This corner frequency must be above the desired –3-dB bandwidth point to avoid attenuating high-frequency audio signals.

Equation 8. GUID-103CDBF5-DE1D-4C6C-9B04-D90513C630C7-low.gif

C3 and C4 are 390-pF capacitors, which places the corner frequency approximately 1 decade above the desired –3-dB bandwidth point. Capacitors C3 and C4 must be NP0 or C0G type ceramic capacitors or film capacitors. Other ceramic dielectrics, such as X7R, are not suitable for these capacitors and produce distortion.