DocID022589 Rev 2

5/15

AN4022

Dynamic resistance and how to measure it

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Dynamic resistance and how to measure it

In the previous section it was shown that the remaining voltage across a circuit to protect is

first parameter is generally well known and specified. In the past dynamic resistance has

been specified but with test conditions different from real surge conditions giving pessimistic

results, especially for short surges like electrostatic discharges. The pulse used had a

duration of 2.5 µs.

To be closer to typical ESD (defined in IEC61000-4-2), a 100 ns pulse width has been

chosen.

An accurate voltage measurement is quite difficult during high rate of rise current, due to the

voltage probing loop inductance, inducing parasitic voltage:

().

So a triangular pulse is used This is shown in Figure 6. No oscillations disturb the

measurement.

The current is measured during the test by a current monitor (Pearson Electronics). The

voltage measurement is by the “Kelvin” method in coaxial configuration in order to get best

accuracy (test board shown in Figure 7). An adequate voltage range and offset is set on the

oscilloscope to get the best dynamic measurement without amplifier saturation.

IPP = 30 A

tP 71 ns

≈

VCL value