SBAA548A April   2022  – May 2022 ADS8588S , ADS8681 , ADS8686S , ADS8688 , ADS8688A

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Circuit Design and Test System
    1. 2.1 Design Description
      1. 2.1.1 Input Protection
      2. 2.1.2 Power Supply Design and Protection
      3. 2.1.3 Digital Isolation Design
      4. 2.1.4 Component Selection and Layout Considerations
    2. 2.2 Test System
      1. 2.2.1 Reference
    3. 2.3 Standards and Test Criteria
  5. 3Test Details and Results
    1. 3.1 Electrical Fast Transients (EFT)
    2. 3.2 Electrostatic Discharge (ESD)
    3. 3.3 Surge Immunity (SI)
    4. 3.4 Conducted Immunity (CI)
    5. 3.5 Radiated Immunity (RI)
    6. 3.6 Radiated Emissions (RE)
      1.      20
  6. 4Schematics
  7. 5PCB Layouts
  8. 6Bill of Materials
  9. 7Acknowledgments
  10. 8References
  11. 9Revision History

2.1.2 Power Supply Design and Protection

The design and protection of the power supply is managed from either the non-isolation or isolation side of the circuit:

  • Non-isolation side

    The low-dropout regulator (LDO), TPS7A4700 (U7), is designed to step down a 6- to 12-V input to +5 V for powering the circuits on the non-isolation side on the test board including the SN6505 (U8) which is a low-noise, low electromagnetic interference (EMI) push-pull transformer driver. A second TPS7A4700 (U9) regulates the U7 output to +3.3 V for the ISO7742 digital isolators (U3 and U5) on the test board.

    A bidirectional TVS diode (MBJ15CA, D18) is used to clamp any high transient or fault signal from external power supply that is applied to the terminal block (J4). The TVS diode is able to clamp a transient voltage higher than 15 V (nominal). A Schottky diode (MBRS4201, D17) is inserted after the D18. Both diodes are intended to prevent potential miswiring from an external power supply connection to the power supply input on J4. The same protection scheme is designed for the power supply on the isolation side.

  • Isolation side

    The power supplies (+3.3 V and +5 V) on the isolation side are generated from two low-dropout regulators (LDOs), U6 and U10, which regulate the output from the transformer (T1) and the SN6505 (U8) which is a low noise, low EMI push-pull transformer driver on the non-isolation side on the test board.

    The TPS7A4700 (U6) generates +5-V power supply for the ADS8686S ADC and REF5025 (U2) voltage reference. The second TPS7A4700 (U10) generates +3.3-V power supply for the ADS8686S (U1) and the digital isolators (U3 and U5) on the isolation side of the test board. The +5-V power supply is protected with a 5.6-V TVS diode (D24), and also the +3.3-V power supply is protected with a 3.9-V TVS diode (D23).

The power supply circuits on the ADS8686S EMC test board are intentionally designed to be compatible with the robust design in a typical industrial system. The ADS8686S EMC test board has an alternative solution powered by two DC power supplies to provide the necessary supplies separately on the isolation and non-isolated side of the test board.