At project review meetings, don't we often hear complaints like this: "I clearly chose a TVS diode rated to withstand 30kV, and the parameters in the datasheet fully comply with the IEC 61000-4-2 Level 4 standard, so why do some boards still crash due to ESD during mass production? Why are even expensive CPUs getting damaged?"

This is probably the most frustrating problem for many hardware engineers. We often put our faith in the eye-catching "30kV" or "15kV" rating on the first page of a datasheet, while overlooking what that TVS actually does during the few nanoseconds when an ESD event occurs.

   Today, let's take a closer look at the most critical yet most frequently misinterpreted "truth mirror" in a TVS datasheet — the TLP curve. By comparing the measured data of international giants and leading domestic brands (such as Shanghai Leiditech), we'll see how to truly select the right "gatekeeper".

I.The Extremely Short Time Window: The Violent Aesthetics of ESD

First, we must clearly understand our opponent. ESD is not a gentle DC power source; it is an extremely high-voltage, high-speed transient energy pulse. According to the IEC 61000-4-2 standard, an 8kV contact discharge waveform has the following extremely stringent characteristics:

l Extremely fast rise time: Rise time is less than 1ns (0.7ns - 1ns).

l Huge peak current: At the first peak, the current can reach tens of amperes (8kV corresponds to approximately 30A peak; 15kV corresponds to approximately 56A peak).

This means that the TVS must transition from a "high-impedance insulator" to a "low-impedance conductor" within approximately 1 nanosecond. If its response is even slightly too slow, the high-voltage spike — thousands of volts — will travel straight into and damage your expensive CPU or FPGA.

II.The "Sweet Trap" in Datasheets: Static Parameters vs. Dynamic Truth

  When we open the datasheet of any TVS, the first things that catch our eye are usually VRWM (reverse stand-off voltage) and VC (clamping voltage). Many engineers believe that as long as the withstand voltage of the downstream chip is higher than VC, the system is safe.

  However, there is a huge cognitive bias here: most of the parameters in the datasheet are measured under "slow" surge conditions (such as 10/1000μs or 8/20μs waveforms), which are completely different from the nanosecond-level impact of ESD. In contrast, the actual IEC 61000-4-2 ESD strike has a rise time of less than 1ns, and its peak current can instantly surge above 30A under 8kV contact discharge.

   In the face of such a massive di/dt, the TVS is no longer an ideal switch, but behaves like a resistor. At this moment, what truly determines success or failure is the dynamic clamping voltage measured under TLP (Transmission Line Pulse) testing.

II.The TLP Curve: Seeing Through the TVS's "Inner Strength" at a Glance

   The TLP curve simulates a real ESD environment. When interpreting the curve, we focus primarily on three core dimensions:

l Slope (dynamic resistance RDYN): The steeper the curve after breakdown (closer to vertical), the lower the dynamic resistance. This means that even as the current surges, the voltage does not increase significantly.

l The 16A Rule: Locate the 16A point on the TLP curve (corresponding to the typical effective current of an 8kV contact discharge). The voltage value at this point is the actual "survival voltage" that your chip will truly withstand.

l Snapback characteristic: An excellent TVS, after being triggered, will rapidly drop back to a lower voltage level. This characteristic is particularly important for high-speed interface protection.

III.Showdown of the Titans: International Brands vs. Shanghai Leiditech

To verify the true performance level of domestic TVS products, we selected mainstream USB 3.0 interface protection solutions on the market and compared the TLP parameters of a leading international brand (using Infineon as an example) against those of Shanghai Leiditech's same-specification products.

Test conditions: IEC 61000-4-2 contact discharge, TLP pulse width 100ns.

From the comparison data, it can be seen that Leiditech's ULC0342CDNH performs excellently in dynamic resistance control. Under a high-current surge of 16A, it firmly clamps the voltage at 9.8V, while the competitor's ESD113-B1-02EL allows the voltage to climb to 14V.For advanced process chips with an absolute maximum voltage rating of only 10V, choosing the competitor's part could mean leaving things to chance, whereas selecting Leiditech provides a definite safety margin. This also breaks the stereotype held by some engineers that domestic TVS devices are "only capable of low-end applications."

IV.Pitfall Avoidance Guide: How to Select Like an Expert?

Based on the above physical characteristics, three principles are crucial in practical design to effectively protect a system from ESD damage:

1、Layout: Minimize "Dynamic Inductance"

No matter how fast the TVS responds, it cannot outrun the parasitic inductance caused by PCB traces. The inductor formula is V = L × di/dt. Under ESD, di/dt is extremely large, and even 1nH of inductance will generate a significant voltage drop.

l Rule: The TVS must be placed as close as possible to the IO port or power pin that needs protection

l Path: Ensure that the via from the TVS to GND is as short and wide as possible. The signal should pass through the TVS first, then go to the downstream chip, using the "branch" principle to divert the energy away.

2、Selection: Not Only Look at VRWM, But Also at VC (at IPP)

Don't just look at static parameters. Go find the clamping voltage waveform diagram for IEC 61000-4-2 or the TLP curve in the datasheet.

• Verify: The clamping voltage at 16A (the typical current corresponding to 8kV contact discharge). This voltage must be lower than the absolute maximum rating of the protected chip (a derating margin of more than 20% is recommended).

3、High-speed signals: Pay attention to capacitance CJ

For HDMI 2.1 (12Gbps) or USB 3.2 Gen 2 (10Gbps) interfaces, traditional TVS devices (with junction capacitance of tens of pF) will directly "eat up" the signal.

l It is essential to select: Low-capacitance TVS (typically <0.5pF) with snapback characteristics, or an ESD suppressor with integrated TVS. The snapback ESD devices developed by Shanghai Leiditech ensure signal integrity while providing extremely low clamping voltage.

ESD protection is not a mystical art, but a battle of nanosecond-level response speed and dynamic resistance.

Through the TLP curve, we can see through the flashy marketing parameters in the datasheet to the true physical characteristics of the device. From the comparison, it can be seen that domestic manufacturers, represented by Shanghai Leiditech, are now capable of competing with international giants in core dynamic parameters, and even have advantages in low clamping voltage and low capacitance control.

As engineers, what we need to do is examine every component with a data-driven perspective, ensuring that when ESD strikes, our system not only "survives" but also remains "completely unscathed."