ESD (Electrostatic Discharge) is a common threat to electronic devices, which can cause chip damage, signal interference and even system failure. Here is the principle of ESD, protection methods, and a comprehensive analysis of key components.
l Static accumulation: Friction, separation (such as human movement, equipment handling) causes charge accumulation (up to several kV).
l Discharge process: When a charged object touches an electronic device, the charge is released instantaneously (as in the human discharge model HBM, it can reach 8kV).
l Instantaneous high voltage: nanos-level pulses with voltages up to tens of kV (but with less energy).
l Damage type:
¢ Hard damage: Gate breakdown, metal melting (permanent damage).
¢ Soft damage: Logic error, parameter drift (potential failure).
Standards | Discharge model | Typical Test levels |
HBM | Mannequin | ±2kV ~ ±8kV |
MM | Machine model | ±200V |
CDM | Charging device model | ±500V ~ ±2kV |
IEC 61000-4-2 | Air/contact discharge | ±4kV ~ ±15kV |
l Ground design: Low impedance ground path to avoid charge accumulation.
l Insulation treatment: Reduce friction (e.g. Anti-static material).
l Structural shielding: Metal enclosure, conductive foam.
l Specialized ESD devices: TVS diodes, TSS, MLV, etc. (core solutions).
l Filter circuit: RC/LC filter to suppress high frequency interference.
l PCB layout optimization: Shorten sensitive signal traces and avoid loops.
Device type | Principle | Response time | Clamping voltage | Capacitor | Applicable scenarios |
TVS diode | Avalanche breakdown | Picosecond level | Low (5V to 50V) | Medium low (0.5 to 50pF) | High-speed interface (USB, HDMI) |
MLV (Multilayer Rheostat | Pressure-sensitive effect | Nanosecond scale | Medium (30V to 100V) | High (~100pF) | Power cord, low frequency signal |
TSS (Semiconductor discharge tube) | Thyristor trigger | Nanosecond level | Low (<10V) | Medium (~50pF) | Communication line (RS485) |
Polymer ESD suppressor | Voltage-triggered conduction | Nanosecond level | Medium high | Extremely low (<0.5pF) | High frequency radio frequency (antenna) |
l Use the avalanche effect of the PN junction to quickly clamp voltage during ESD events.
l Unidirectional TVS: For DC circuits (such as power supply).
l Bidirectional TVS: For AC/differential signals (such as USB, HDMI).
Parameters | Instructions | Sample values (USB protection) |
V_{WM} | Working voltage (not conducting in normal state) | 5V |
V_{BR} | Breakdown voltage (minimum trigger voltage) | 6V |
V_{CL} | Clamping voltage (peak voltage during ESD) | 10V (8kV ESD) |
I_{PP} | Peak pulse current | 5A (8kV ESD) |
C_{junction} | Junction capacitance | 1pF (Low capacitance for high-speed interfaces) |
l V_{WM} ≥ the working voltage of the circuit (for example, 5.5V TVS for a 5V circuit).
l V_{CL} < the withstand voltage of the protected chip (for example, the withstand voltage of the MCU IO port 12V, select V_{CL} < 10V).
l Capacitance matching: Low capacitance TVS for high frequency signals (e.g. USB 3.0 requires <0.5pF).
l Features: Strong current-carrying capacity, but high capacitance, suitable for power ports.
l Features: Ultra-low capacitance (<0.1pF), suitable for RF antennas.
l Features: TVS + filter + current limiting integrated (such as USB3.0 protection chip).
1 USB_D+ → [TVS (0.5pF)] → [22Ω resistor] → MCU
2 USB_D- → [TVS (0.5pF)] → [22Ω resistor] → MCU
l TVS: Clamp ESD voltage.
l Resistor: Current limiting + absorbs energy in conjunction with TVS.
1 VCC → [MLV] → [LC filter] → [TVS] → Chip
l MLV: Absorb medium-voltage surges.
l TVS: Fine clamping.
l Error 1: Relying solely on TVS while neglecting PCB layout (long traces increase the risk of ESD coupling).
l Error 2: High TVS capacitance causes signal distortion (such as selecting >1pF TVS for HDMI).
l Error 3: Without considering system-level grounding, ESD current cannot be discharged effectively.
l ESD protection core: Low clamping voltage, fast response, low capacitance.
l Preferred option:
¢ High speed signal → ultra-low capacitance TVS/ polymer ESD suppressor.
¢ Power/Low frequency → MLV/TSS.
¢ High integration → protection + filter chip.
l Test verification: Passed IEC 61000-4-2 contact/air discharge test (±8kV).
If specific device recommendations or circuit optimizations are required, application scenarios (such as interface type, working voltage, etc.) can be provided!
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