Every connector on your board is an antenna for trouble. A user touching a USB port can inject kilovolts of electrostatic discharge (ESD), and long cables or inductive loads can add surges that last microseconds to milliseconds. A transient voltage suppressor (TVS) diode is the simplest way to keep those events away from your IC pins.
How a TVS diode works
A TVS is a silicon junction that sits in parallel with the line you protect. Under normal operation it is high impedance. When voltage exceeds its breakdown level, it avalanches and clamps the line, shunting the energy to ground. When the event ends, it recovers on its own, with no fuse to replace.
Key parameters
- Standoff voltage (VRWM): the maximum working voltage with negligible leakage. Choose it at or above your signal or rail voltage.
- Breakdown voltage (VBR): where conduction begins, typically 5-10% above standoff.
- Clamping voltage (VC): the voltage seen by your circuit at a specified peak pulse current. This must stay below the absolute maximum rating of the protected device.
- Peak pulse power or current (IPP): surge capability, usually rated on an 8/20 us waveform. ESD ratings follow IEC 61000-4-2 (contact and air discharge).
- Capacitance: critical for high-speed lines. USB 3, HDMI and Ethernet need low-capacitance arrays, often below 1 pF, while power rails can use large, rugged parts.
- Unidirectional vs bidirectional: use unidirectional for DC rails and single-ended signals, bidirectional for AC or signals that swing negative.
Layout matters as much as the part
Place the TVS as close to the connector as possible, before any series components. Route the signal through the TVS pads rather than stubbing off it, and use a short, wide, low-inductance path to a solid ground. Even a few millimeters of trace adds inductance that produces a voltage spike during a fast ESD edge, defeating a perfectly good diode.
Choosing a part
Start from the interface: find the maximum signal voltage, the data rate (which limits capacitance), and the required standard level, such as 8 kV contact ESD or a surge rating for industrial ports. Then verify the clamping voltage against the protected IC's limits. If you are sourcing parts, a reliable TVS diode supplier will list these parameters clearly so you can filter by standoff voltage, package and capacitance: TVS diode supplier.
Summary
Pick standoff voltage just above your operating voltage, check that the clamp voltage is safe for the downstream IC, match capacitance to your data rate, and place the device right at the connector. Then test with an ESD gun if you can.
Top comments (0)