| Operating Principle | Protection function | A transient-voltage-suppression diode diverts excessive transient current away from a protected circuit. | Connect the device in parallel with the circuit or signal pair being protected. |
| Normal-voltage state | The TVS remains in a high-impedance state when the applied voltage is below its breakdown region. | Choose a working standoff voltage higher than the circuit's maximum continuous voltage. |
| Transient state | When a surge exceeds the breakdown region, the diode conducts heavily and clamps the voltage. | Verify that the maximum clamping voltage is below the protected component's absolute maximum rating. |
| Response speed | TVS diodes respond very quickly, commonly within the sub-nanosecond to nanosecond range, depending on construction and test conditions. | Use low-inductance placement because PCB trace inductance can create additional voltage during a fast surge. |
| Energy conversion | The surge energy is mainly converted into heat within the TVS junction. | Match the pulse-power and pulse-energy capability to the expected surge waveform and repetition rate. |
| Reset behavior | After the transient ends and the temperature returns to a safe level, the device normally returns to its high-impedance state. | A TVS is generally a clamping device, not a substitute for a fuse or circuit breaker. |
| Key Electrical Ratings | VRWM: Working Standoff Voltage | The maximum continuous reverse voltage that can be applied without significant avalanche conduction. | Select VRWM above the highest normal DC voltage or the peak value of the normal AC waveform. |
| VBR: Breakdown Voltage | The voltage range at which the specified test current flows and avalanche conduction begins. | VBR is higher than VRWM and is not the same as the final clamping voltage. |
| VC: Maximum Clamping Voltage | The maximum specified voltage across the TVS at a stated peak pulse current. | Compare VC with the protected IC, transceiver, sensor, or power rail's maximum allowable voltage. |
| IPP: Peak Pulse Current | The peak current associated with the specified surge test waveform, often a standardized 10/1000 μs waveform for power TVS ratings. | Do not compare IPP values without checking the test waveform and duration. |
| PPPM: Peak Pulse Power | The rated peak pulse power, commonly approximated under the specified test condition as PPPM = VC × IPP. | Use the manufacturer's derating curve for temperature, pulse duration, and repeated surges. |
| IR: Reverse Leakage Current | The current flowing through the device at a specified reverse voltage below breakdown. | Low-leakage versions are preferable for battery-powered circuits and high-impedance signal lines. |
| Capacitance | Junction capacitance can range from less than 1 pF for specialized high-speed parts to hundreds or thousands of pF for higher-power devices. | Choose low capacitance for high-speed interfaces; check capacitance at the specified bias voltage and frequency. |
| Device Configuration | Unidirectional TVS | Acts like a conventional rectifier in the forward direction and clamps positive transients through avalanche action. | Commonly used on DC power rails and circuits where the signal polarity is always positive. |
| Bidirectional TVS | Provides similar avalanche clamping for positive and negative transients. | Suitable for bipolar signals, differential pairs, and AC lines when symmetrical protection is required. |
| Single-line protector | Protects one conductor relative to ground or a return path. | Use when the protected path and grounding arrangement are clearly defined. |
| Multiline array | Integrates multiple TVS elements in one package for several signal or data lines. | Check channel-to-channel matching, common-mode behavior, capacitance, and pin assignment. |
| Power TVS versus data-line TVS | Power devices prioritize surge-current capability; data-line devices prioritize low capacitance and signal integrity. | Select according to both electrical stress and bandwidth requirements rather than peak-power rating alone. |
| Example Selection Targets | 5 V DC rail | A typical design may consider VRWM values around 5 V to 6 V, subject to the rail's actual tolerance and transients. | Ensure the selected VC remains below the protected circuit's absolute maximum input voltage. |
| 12 V DC rail | A typical design may consider VRWM values around 12 V to 15 V, depending on charging voltage and operating tolerance. | Account for the highest charger, alternator, adapter, or load-dump-related voltage that can occur in the system. |
| 24 V DC rail | A typical design may consider VRWM values around 24 V to thirty-three V, depending on the permitted operating range. | Do not select solely from the nominal voltage; calculate the actual maximum continuous voltage first. |
| High-speed differential data pair | Typical priorities are very low capacitance, controlled leakage, matched channels, and low dynamic clamping voltage. | Confirm that insertion loss, return loss, common-mode capacitance, and data rate meet the interface requirements. |
| Unregulated or inductive load | The circuit may experience repetitive switching spikes with different energy and duration from a standardized surge. | Evaluate repetitive pulse heating and consider combining the TVS with a fuse, series impedance, snubber, or controlled switching method. |
| PCB Installation | Placement distance | The protector should be placed close to the connector or entry point where the transient enters the board. | Minimize the distance between the protected line, TVS, and return path. |
| Trace inductance | Fast current changes across trace inductance create an additional voltage, expressed approximately as V = L × di/dt. | Use short, wide traces or planes, avoid unnecessary vias, and keep the surge-current loop compact. |
| Ground or return path | The diverted surge current must flow through a low-impedance return path. | Avoid routing the surge current through sensitive ground sections, measurement references, or protected IC grounds. |
| Polarity and orientation | Unidirectional devices have a defined cathode and anode orientation; bidirectional devices are generally not polarity-sensitive for normal operation. | Follow the circuit schematic and package marking, especially for DC power protection. |
| Thermal and mechanical layout | The package, copper area, ambient temperature, and pulse repetition affect temperature rise and reliability. | Use the recommended land pattern and derating information; keep high-energy devices away from heat-sensitive parts. |
| Connector protection | External cables can conduct electrostatic-discharge and electrical-fast-transient energy into the product. | Place the TVS before long board traces and coordinate it with shield, chassis, and signal-return design. |
| Verification | Surge waveform | Common evaluations include electrostatic discharge, electrical fast transients, surge pulses, and switching transients. | Test using the waveform, amplitude, source impedance, polarity, and repetition rate required by the product environment. |
| Protected voltage | Measure the voltage directly at the protected component pins, not only at the TVS terminals. | This reveals the effect of PCB inductance and layout-related overshoot. |
| Signal integrity | Protection components can add capacitance, leakage, insertion loss, and discontinuities. | Verify eye diagrams, error rate, bandwidth, and communication stability after installation. |
| Failure inspection | An overstressed TVS may become short-circuit, open-circuit, or electrically degraded depending on the event. | Inspect leakage, clamping behavior, continuity, and nearby components after abnormal surge testing. |
