SBASAZ0 August   2024 AMC0136

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  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 (DEN Package)
    5. 5.5 Package Characteristics
    6. 5.6 Electrical Characteristics
    7. 5.7 Switching Characteristics
    8. 5.8 Timing Diagram
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Analog Input
      2. 6.3.2 Modulator
      3. 6.3.3 Isolation Channel Signal Transmission
      4. 6.3.4 Digital Output
        1. 6.3.4.1 Output Behavior in Case of a Full-Scale Input
        2. 6.3.4.2 Output Behavior in Case of a Missing High-Side Supply
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
      3. 7.2.3 Input Filter Design
      4. 7.2.4 Bitstream Filtering
    3. 7.3 Best Design Practices
    4. 7.4 Power Supply Recommendations
    5. 7.5 Layout
      1. 7.5.1 Layout Guidelines
      2. 7.5.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information
    1. 10.1 Mechanical Data

7.2.3 Input Filter Design

Place a RC filter in front of the isolated amplifier to improve signal-to-noise performance of the signal path. Input noise with a frequency close to the ΔΣ modulator sampling frequency (typically 10MHz) is folded back into the low-frequency range by the modulator. The purpose of the RC filter at the input is to attenuate high-frequency noise below the desired noise level of the measurment. In pactice, a cutoff frequency that is two orders of magnitude lower than the modulator frequency yields good results.

Most voltage-sensing applications use high-impedance resistive dividers in front of the isolated modulator to scale down the input voltage. In this case, a single capacitor (as shown in Figure 7-2) is sufficient to filter the input signal. Assuming a 10kΩ sensing resistor (R2), a 100pF filter capacitor yields in a 160kHz cutoff frequency.

AMC0136 Input Filter Figure 7-2 Input Filter