AN3353

Clamping voltage measurement

Doc ID 018527 Rev 1

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Clamping voltage measurement

As we say in Section 1: Contact discharge or air discharge?, the clamping voltage

measurement is done in contact mode at

±8 kV. The ground return of the ESD gun is

connected directly to the GND test PCB, as well as the reference of the oscilloscope.

A 3 GHz analog bandwidth oscilloscope is used (2 GHz minimum is recommended by the

standard). Its sample rate is 20 giga samples per second and the time base is set to

20 ns/div. The vertical amplifier input impedance is set to 50

Ω.

A 50

Ω coaxial cable is connected to the SMA where the clamping voltage is measured

(Figure 3). Depending on the device and the test conditions, the clamping voltage can vary

between several volts up to around two hundred volts. So attenuators are inserted at the

end of the cable at the channel oscilloscope input. Two -20 dB attenuators in series give an

attenuation ratio of 100.

A clamping voltage waveform example is shown in Figure 4. On the waveform, we find the

typical clamping voltage at three different times after the beginning of the surge: t = 30 ns,

t = 60 ns and t = 100 ns. The typical peak voltage is also noted.

According to the JESD210 Jedec standard, a limiting resistor can be added in series with

the measurement cable. In this case, its value is specified.

Figure 4.

Clamping voltage waveform example