ESD Protection Calculator

ESD model IEC 61000-4-2 (system) HBM (device handling)

Select the discharge model to estimate stress.

ESD voltage (kV)

Typical IEC levels: 2, 4, 8, 15 kV.

Pin max current (mA)

Use absolute max or safe injection limit.

System max voltage (V)

Highest expected signal or supply level.

TVS clamp voltage (V)

Approx clamp at ESD current, not stand-off.

Series resistor installed (Ω)

Includes any effective series resistance.

Trace length to TVS (mm)

Long traces increase inductive overshoot.

Trace width (mm)

Wider return paths generally reduce inductance.

Ground/return quality Excellent (solid plane, tight return) Good Fair Poor (long loops, gaps)

Impacts clamp effectiveness and overshoot.

Chassis bond near entry Yes No

Directs current away from sensitive circuitry.

Chassis/guard keepout (mm)

More distance reduces arc and coupling risk.

Relative humidity (%)

Dry air raises charging and event severity.

ESD mat in use Yes No

Handling control for assembly and debug.

Wrist strap in use Yes No

Reduces device handling risk.

Packaging type Shielded bag Pink anti-static None

Shielding reduces exposure during transport.

Environment Office / mixed Electronics lab Dry factory floor Field service

Dry, uncontrolled sites raise overall risk.

Submit Reset

Result appears above this form after submit.

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Discharge models and test levels

IEC 61000-4-2 uses a 150 pF capacitor and 330 Ω source resistance, so an 8 kV strike implies an initial peak near 24 A typically before layout effects. Many products target 8 kV contact and 15 kV air on user-accessible ports, while assembly handling is often screened with HBM levels such as 1–2 kV. Selecting the model aligns peak current and stored energy estimates with the scenario.

TVS clamp behavior and voltage headroom

A TVS is effective when its dynamic clamp stays below the protected pin’s tolerance at high current, not merely below the normal rail. For low-voltage logic, teams often accept a clamp 2–3× the rail and rely on series impedance plus tight returns to keep pin current under the injection limit. If clamp voltage approaches the system max, usable margin drops and the score reflects that.

Series resistance and current limiting

With a clamped node, the approximate pin current is (Vclamp − Vsystem)/(Rsrc + Rseries). For a 12 V clamp and 5 V system, the 7 V stress must be shared by the source and series resistance. To stay under 10 mA with a 330 Ω source, total resistance needs about 700 Ω, meaning roughly 370 Ω extra series resistance. The tool reports the required value so you can balance protection and signal integrity.

Layout inductance and overshoot control

Fast edges make inductance critical. A few centimeters of narrow trace can add tens of nanohenries, and 10 nH with a 30 A/ns edge can create hundreds of volts in the local loop. The calculator uses a width-scaled rule-of-thumb inductance to estimate overshoot, then penalizes the score when overshoot nears the clamp voltage. Short placement, wide returns, and stitching vias near the TVS usually yield the biggest gains.

Process controls, humidity, and readiness scoring

ESD programs reduce event rates as well as damage severity. Relative humidity above ~40% lowers charging for many materials, while mats, wrist straps, and shielded packaging reduce handling exposure. The readiness score blends electrical margin, overshoot, layout practices, and handling controls into one screening number. Use it to rank options, document tradeoffs, and decide when full gun testing is justified.

1) Is this score a compliance certification?
No. It is a screening metric built from simplified electrical and process assumptions. Use it to compare design options, then confirm with lab ESD gun testing and product-specific acceptance criteria.

2) Why can overshoot exceed the TVS clamp voltage?
Overshoot comes from inductance in the discharge loop. The TVS may clamp at its terminals, but voltage can rise elsewhere due to L × di/dt. Short loops, wide returns, and close placement reduce this.

3) What TVS clamp voltage should I enter?
Use a realistic dynamic clamp value at ESD current from the datasheet curves, not the stand-off rating. If only typical data is available, choose a conservative value to avoid overstating margin.

4) How do I choose the pin max current limit?
Start with the device’s absolute maximum injection or clamp current rating. If uncertain, pick a lower engineering limit and rerun the calculator to see how much extra series resistance or layout improvement you need.

5) When is a series resistor more useful than a stronger TVS?
If your interface tolerates added impedance, series resistance directly limits current into the IC under a clamp condition. A stronger TVS helps too, but placement and return inductance can dominate the outcome.

6) Which inputs usually move the score most?
TVS placement/trace length, return quality, chassis bonding, and humidity/handling controls often dominate. After that, series resistance and clamp voltage set the electrical margin that determines whether the pin current stays safe.