JAJSS82E August   2009  – July 2024 LPV521

PRODUCTION DATA  

  1.   1
  2. 1 特長
  3. 2 アプリケーション
  4. 3 概要
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
    4. 6.4 Device Functional Modes
      1. 6.4.1 Input Stage
      2. 6.4.2 Output Stage
  8. 7 Applications and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Driving Capacitive Load
      2. 7.1.2 EMI Suppression
    2. 7.2 Typical Applications
      1. 7.2.1 60Hz Twin T-Notch Filter
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
        3. 7.2.1.3 Application Curve
      2. 7.2.2 Portable Gas Detection Sensor
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
        3. 7.2.2.3 Application Curve
      3. 7.2.3 High-Side Battery Current Sensing
        1. 7.2.3.1 Design Requirements
        2. 7.2.3.2 Detailed Design Procedure
        3. 7.2.3.3 Application Curve
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 ドキュメントの更新通知を受け取る方法
    4. 8.4 サポート・リソース
    5. 8.5 Trademarks
    6. 8.6 静電気放電に関する注意事項
    7. 8.7 用語集
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.1.2 Detailed Design Procedure

The notch frequency is set by F0 = 1 / 2πRC. To achieve a 60Hz notch, use R = 10MΩ and C = 270pF. If eliminating 50Hz noise, which is common in European systems, use R = 11.8MΩ and C = 270pF.

The twin T notch filter works by having two separate paths from VIN to the amplifier input. A low-frequency path through resistors R-R and another separate high-frequency path through capacitors C-C. However, at frequencies around the notch frequency, the two paths have opposing phase angles and the two signals tend to cancel at the amplifier input.

To ensure that the target center frequency is achieved, and to maximize the notch depth (Q factor), balance the filter as much as possible. To obtain circuit balance, while overcoming limitations of available standard resistor and capacitor values, use passives in parallel to achieve the 2C and R/2 circuit requirements for the filter components that connect to ground.

To ensure that passive component values stay as expected, clean the board with alcohol, rinse with deionized water, and air dry. Ensure that the board remains in a relatively low humidity environment to minimize moisture that can increase the conductivity of board components. Also large resistors come with considerable parasitic stray capacitance; the effects can be reduced by cutting out the ground plane below components of concern.

Use Large resistors in the feedback network to minimize battery drain. When designing with large resistors, consider the resistor thermal noise, op-amp current noise, as well as op-amp voltage noise in the noise analysis of the circuit. The noise analysis for the circuit in Figure 7-3 can be done over a bandwidth of 5kHz, which takes the conservative approach of overestimating the bandwidth (LPV521 typical GBW/AV is less). The total noise at the output is approximately 800µVPP, which is excellent considering the total consumption of the circuit is only 540nA. The dominant noise terms are op-amp voltage noise (550µVPP), current noise through the feedback network (430µVPP), and current noise through the notch filter network (280µVPP). Thus, the total circuit noise is less than ½ LSB of a 10-bit system with a 2V reference, which is 1mV.