ESD protection
Contents
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
- Ultra-low: < 0.5pF
- Low: 0.5pF to 1.5pF
- 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)