What a TLP Report Can and Cannot Prove About an ESD Diode Supplier

A transmission line pulse report can show how an ESD protection diode conducts, clamps, and eventually changes under a defined device-level pulse. It cannot, on its own, prove that a finished product will pass a stated IEC 61000-4-2 level. A useful supplier review therefore starts with the test conditions and failure criterion, not with the largest current printed beside the curve.

That distinction matters during component approval. Two reports may both carry the label “TLP,” yet use different pulse widths, rise times, sampling windows, fixtures, temperatures, and definitions of failure. Putting their It2 values into a ranking table would create a precise-looking comparison with no controlled basis.

Read the report header before reading the curve

The first review pass should be almost boring. Identify the document version, full ordering code, sample lot, test method, and laboratory. Then check whether the report states the TLP pulse width and rise time. ANSI/ESD STM5.5.1-2022 establishes a device-level method for TLP testing and reporting, but a supplier still needs to disclose the settings used for the submitted data.

Record these fields before extracting any electrical value:

• complete part number, package, polarity, and sample lot;

• number of devices tested and whether individual or averaged curves are shown;

• pulse width, rise time, current step, and measurement window;

• ambient or chuck temperature and preconditioning, if any;

• voltage used for leakage checks before and after stress;

• the rule used to mark failure or It2;

• fixture, reference plane, and any de-embedding applied to the result.

Missing fields do not automatically make the curve false. They make it difficult to reproduce and unsuitable for a controlled supplier comparison. A cropped chart without a method statement may help an engineer ask the next question, but it should not close an AVL review.

Treat It2 as a report-defined event

It2 is often used for the current at which second breakdown or another defined failure indication occurs. The exact marker still has to be read from the report. The last visible point is not always the failure point. A foldback in the current-voltage curve may need confirmation from a leakage check, a short-circuit measurement, or another electrical criterion.

The practical review question is not “How many amperes is It2?” It is “What observation caused the laboratory to call this point It2?” If the report used a leakage threshold, request the bias voltage and the before-and-after values. If it used a sudden voltage change, ask whether the sample remained functional after the pulse. If different samples failed by different modes, an average It2 can hide information that matters to qualification.

Sample count also changes the meaning of the number. One device can reveal a characteristic curve. It cannot establish a production distribution. For supplier approval, show individual devices or at least a range, identify the lots, and keep outliers visible. Removing a low result needs a documented technical reason rather than an unlabeled “data cleaning” step.

Dynamic resistance depends on the fitted region

Dynamic resistance is commonly estimated from the slope of a selected conducting region:

Rdyn ≈ ΔV / ΔI

The equation is simple; selecting the region is not. A snapback device may have a trigger region, a transition, and a later portion that is closer to linear. Fitting points across all three regions produces a value that does not describe any one of them. A supplier report should therefore mark the fitted current range or provide enough raw points for the reviewer to reconstruct it.

ASIM uses the same rule when reviewing its own ESD diode data for an application: compare dynamic resistance only when the pulse method, temperature, and fit range match. A smaller value extracted from a different region is not automatically the stronger protection option. Working voltage, leakage, capacitance, package parasitics, and clamp voltage at the required current still govern whether the device belongs on the candidate list.

Why a TLP current is not an IEC voltage

IEC 61000-4-2:2025 addresses system-level immunity of electrical and electronic equipment. The discharge is applied to a finished device or to a coupling structure under a specified setup. Current can flow through the enclosure, connector, cable shields, PCB reference planes, protection device, power network, and unintended parasitic paths.

A TLP setup examines a component or test structure with a controlled device-level pulse. Even if the two waveforms share a similar time scale in part of their response, their sources, fixtures, current distributions, and pass criteria are not interchangeable. There is no generally valid formula that converts an It2 current into “8 kV IEC” or another finished-product rating.

The separation becomes obvious on a real board. The protection diode may show a reasonable voltage at its own pads while the protected IC pin sees a larger transient. Trace inductance adds voltage during the fast current edge. Ground-path inductance raises the local reference. A cable shield or enclosure seam can inject current into another circuit after the diode has already done its intended job.

Use TLP data to choose and compare candidates. Use system testing to approve the assembled product.

Build a supplier comparison that survives review

A controlled comparison has three gates. The first gate removes parts that do not meet the normal operating window. Verify reverse working voltage, polarity, leakage under bias, line capacitance, and package connection. There is no reason to compare It2 for a diode that would load the signal or conduct during normal operation.

The second gate compares device-level pulse behavior. Use the same TLP method and fit rules. Keep the raw or individual curves when possible. Record clamp voltage at comparable currents rather than taking one convenient point from each chart.

The third gate is an application test on the target board. Measure at the protection device and near the protected IC. For a high-speed interface, add insertion-loss, return-loss, eye, or error-rate checks appropriate to that link. For a high-impedance analog node, measure leakage-related offset over temperature. The result belongs to that PCB revision, placement, and part lot.

The approval record should contain:

1. a traceable component data set with its method and sample identification;

2. an explicit comparison range for clamp voltage and dynamic resistance;

3. post-stress electrical checks and the definition of failure;

4. target-board measurements at named locations;

5. the system ESD configuration, functional criterion, and observed result;

6. a list of changes that require re-evaluation, such as die, package, or layout changes.

This record is more useful than a one-page scorecard. When a supplier updates a die or the PCB team moves the diode, the engineers can identify which evidence is no longer transferable.

Questions to send back to the supplier

If a TLP report raises doubts, ask narrow questions. “Please provide more data” often produces another brochure. Better questions include:

• Which pulse width and rise time produced this curve?

• Is each line an individual device, a typical sample, or an average?

• Which current range was used to calculate dynamic resistance?

• What exact electrical change defines It2 in this report?

• At what bias was post-stress leakage measured?

• Were all samples from one wafer or assembly lot?

• Can the clamp voltage points be supplied in tabular form?

The answers should be retained with the report. Verbal explanations are difficult to audit after a supplier or engineering contact changes.

Does a higher It2 always mean a better ESD diode?

No. A candidate also has to meet the normal voltage, leakage, capacitance, polarity, package, and clamp-voltage requirements. It2 values are comparable only when their methods and failure criteria match.

Can a supplier claim an IEC level from TLP data alone?

TLP data can support component selection and modeling. A system-level IEC result requires the finished product, specified setup, discharge points, operating states, and functional criteria. The report should keep those claims separate.