Q: How to perform ESD protection design for products passing IEC 61000-4-2?
Answer
IEC 61000-4-2 ESD test levels: contact discharge +/-4 kV (level 2) +/-6 kV (level 3) +/-8 kV (level 4); air discharge +/-8 kV (level 2) +/-15 kV (level 3). Protection design: (1) TVS diodes: bidirectional with standoff voltage >= supply voltage and clamping voltage < protected IC max rating. (2) Selection: for USB/ETHERNET use low-capacitance TVS (<1 pF). For GPIO use standard TVS (5-10 pF). For power rails use high-power TVS (SMC or unidirectional). (3) Series resistance: add 33-330 Ohm in series between connector and protected IC to limit ESD current. (4) Ground reference: TVS must have a low-impedance path to chassis/earth ground. Use multiple vias to ground plane. (5) PCB guard ring: add a coplanar guard ring around the protected net connected to GND. (6) Layout: keep TVS within 5 mm of the connector. (7) Air discharge: design enclosure to direct air discharge away from sensitive circuits. (8) Testing: use ESD gun in contact mode - verify functionality after each discharge level.
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