ESD protection

Reference video

1. ESD/Surge Protection Basics

ESD explanation
Electrostatic Discharge, a sudden release of elctricity from one charge object to another, when objects come into contact
  • ICs typicallly very sensitive to ESD, often interfaced to ‘outside world’ via connectors.
  • often use TVS diode or ESD diode to avoid this issue.

2. TVS Diode Operation

TVS Diode Operation

3. TVS Diode parameters

1. Uni- or Bi-directional
  • Uni-directional:
    • Asymmetric I-V curve
    • Protect signal lines that are always above/below reference
  • Bi-directional:
    • Symmetric I-V curve
    • Protect signal lines that can swing above/below reference
2. Number of channels
  • number of TVS diodes contained in a single package
  • typically pacakged for various interfaces (e.g. USB, HDMI, etc.)
3. Working voltage
  • ${V}_{RWM}$
  • recommended operating voltage of TVS diode
  • signal voltage should not exceed working voltage

for example a 3v3 MCU’s I2C connections -> choose a minimum 3v3 working voltage TVS diode

4. Clamping voltage
  • when ESD event occurs, the TVS diode will ensure ‘downstream’ connected devices only see the clamping voltage
  • Downstream devices need to be transmission-line-pulse (TLP) rated for clamping voltage
    • not absolute maximum rated
    • TLP rated can be hard to find in datasheet
    • try to find smallest clamping voltage TVS diode that can meet your needs
5. Capacitance
  1. Ultra-low: < 0.5pF
  2. Low: 0.5pF to 1.5pF
  3. General purpose: > 1.5pF
  • Very important parameter for high-speed interfaces
    • decreases rise/fall time
    • degrading SI

Source impedance & capacitance of TVS diode -> low-pass filter, which is bad for high-speed interfaces

6. IEC 61000-4-2 rating

Robustness rating of protection device

4. Example: Choosing a Suitable TVS Diode & Layout

Connector -> ESD protection -> filtering -> IC

  • ESD protection as close as reasonable to connector
  • Low-inductance connections (short and wide traces)