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

2.1.1 Input Protection

The analog input on each channel of the ADC is protected with a bidirectional transient voltage suppressor (TVS) diode (SMBJ10CA from Littelfuse®) from a transient signal, and a positive temperature coefficient (PTC) resettable fuse (PTS120660V010 from Eaton®) is placed in series with the analog input to limit the transient current under an EMC test condition. The PTC fuse is a device that exhibits a low resistance under a normal condition and exhibits a high resistance in response to an overcurrent. The PTC stands for Positive Temperature Coefficient, so the PTC resistance increases with the increase of temperature. Under a test condition with high transient signals, the self-heating of the resistor causes the resistance to pass a trip point and the resistance dramatically increases. The large tripped resistance effectively limits the high transient current. Once the fault condition is removed, the PTC returns to a low-resistance state; however, the device has a hysteresis and it takes some time to reach a low-resistance value.

A 250-V, high-voltage, C0G type, 15-nF ceramic capacitor is designed on each analog channel of the ADC and placed next to the input terminal blocks so that the transient energy can be discharged to the ground through the shortest path.