Adding a transient-voltage-suppression diode to a connector is a common protection measure. A less obvious step is checking whether the voltage that remains during a transient is acceptable for the circuit behind it.
The voltage in a product name is not enough to make that decision. Three datasheet parameters describe different operating conditions.
Read the three voltages separately
| Parameter | What is tells you | Design question |
|---|---|---|
| Reverse working or standoff voltage, VRWM | Intended normal operating range, with specified leakage | Does this cover the highest normal line voltage? |
| Breakdown voltage, VBR | Avalanche voltage measured at a specified test current | Under what test conditions does significant conduction begin? |
| Clamping voltage, VCL | Voltage across the device at a specified pulse current and waveform | Can the downstream circuit tolerate this residual voltage? |
Nexperia’s TVS selection guide explains these distinctions and the importance of pulse conditions and temperature. Always read the conditions next to a voltage specification
A worked compatibility check
For a public component example, TI lists the TVS1801 with an 18 V standoff voltage and a 27.4 V clamping voltage at 30 A with an 8/20 µs surge waveform. These are different specifications for the same device. TI TVS1801 product information
Now consider a hypothetical downstream input whose absolute maximum is 24 V and which has no separately specified transient tolerance. At that stated pulse condition, a 27.4 V clamp would exceed the input’s limit by 3.4 V, even before additional layout effects. This combination therefore cannot be justified simply because the normal supply is below 18 V.
The component is not inherently unsuitable: its suitability depends on the protected circuit and the expected event. At another pulse current, consult the relevant characteristics rather than reusing the 27.4 V figure. Check whether quoted values are typical or guaranteed over the required conditions.
Specify the event before comparing candidates
Write down the expected pulse polarity, waveform, source impedance, peak current, repetition and operating temperature. A headline pulse-power rating without its waveform is an incomplete comparison. ESD and longer surge pulses are different stresses; a rating for one does not establish performance for the other.
For signal lines, also check capacitance and leakage against the interface requirements. For a sustained overvoltage, plan an appropriate limiting or disconnect function: a pulse-rated TVS is not automatically a continuous voltage regulator. Nexperia’s ESD application handbook provides broader protection-design context.
Review the current path on the PCB
A low clamping voltage at the device does not guarantee the same peak voltage at the protected pins. Interconnect inductance produces an additional voltage proportional to L * di/dt. Trace the path from the entry point through the TVS and its return, and check the connection to the protected circuit. Keep the shunt path short and low-inductance, and avoid sharing an unnecessarily long return with sensitive circuitry. TI discusses these effects in its power-path transient-protection layout guidance.
Before release, record the normal-voltage limit, the relevant clamp specification and the protected input’s allowable voltage in one table. Validate the assembled circuit under its specified test conditions, measuring at the protected pins as well as considering TVS survival.
The useful habit: select a protection device by the voltage and current the complete circuit will experience, not by a matching voltage label.