TVS Diodes and ESD Protection Devices

Both clamp the line once the voltage passes a set threshold. A TVS diode is sized for surge energy and rated in peak pulse power and Ipp at a stated waveform. An ESD diode is sized for a fast static discharge, rated in kV of air and contact discharge, and is built for much lower capacitance. Choose by the event the port faces, then by the capacitance the line can tolerate.

Use a unidirectional part on a DC rail that never goes negative; it also holds a negative transient at its forward voltage. Use a bidirectional part on any line that swings both sides of ground, such as AC signals, transformer-coupled differential pairs and CAN or RS-485 buses whose common mode range extends below ground. A unidirectional part on such a line conducts on every negative excursion and distorts the signal.

They rise in that order. VRWM is the highest voltage the part holds with only leakage current flowing, breakdown voltage is where conduction starts at a small test current, and clamping voltage is what remains across the part at a stated peak pulse current. Put VRWM above your maximum working voltage and check that the clamping voltage at your expected Ipp stays below what the protected IC survives.

Often yes. The transformer isolates the line and rejects much of the common mode energy, but differential surge and energy coupled through the windings still reach the PHY. Whether an Ethernet TVS diode is needed depends on the surge level the port must pass and on the PHY's own rating, so check both before leaving it out.

Close to where the transient enters, with a short, wide return path. On the PHY side of the magnetics, a low capacitance Ethernet ESD protection diode array across the MDI pairs is a common arrangement; parts on the cable side must also respect the isolation rating of the port. Check the PHY vendor's reference design, because the recommended position differs between PHYs.

It depends on the data rate. USB 2.0 data lines leave more room than USB 3.x SuperSpeed pairs, where sub-picofarad parts are the norm. Read the capacitance at the bias and frequency the datasheet states, then confirm with an eye diagram on the finished board.

They are widely used series names tied to package size: SMAJ to the SMA outline (DO-214AC), SMBJ to SMB (DO-214AA) and SMCJ to SMC (DO-214AB). The larger outline carries a higher peak pulse power rating. The prefix tells you the package and power class, not the exact ratings, so compare VRWM, clamping voltage and Ipp in the datasheet.

Send the candidate part number, quantity and the date you need parts. If you are still choosing, describe the port, its working voltage, the ESD or surge level it must pass and the data rate. Samples are available for evaluation, and selected parts are free of charge. Our FAE team will be glad to confirm the options for your project.