ELECTROMAGNETIC COMPATIBILITY AND MEDICAL DEVICES - Design and Development of Medical Electronic Instrumentation - page 173

fingertip of a
standing person delivered to a device, modeled here by a 150-pF capacitor discharged
through a switching component and a 330-

The human body model of Figure 4.18 represents the discharge from the fi

series resistor into the device under test. This
model, which hasn't changed much since it was developed in the nineteenth century, was
originally used to investigate explosive gas mixtures in mines. An ESD simulator is not
more than an instrument implementing this model. A high-voltage power supply is used to
charge a 150-pF capacitor via a charging resistor. The capacitor's charge is then delivered
to the device under test by way of a 330-

Ω

resistor. The switch may be a vacuum relay, a
high-voltage semiconductor switch, or a spark gap.
Construction of the ESD simulator should enable it to generate a discharge waveform
with the parameters shown in Table 4.7. Obviously, the most critical design consideration
is being able to generate the ESD with a rise time of 0.7 to 1 ns. The frequency content of
such an ESD waveform is

Ω

fl flat to around 300 MHz before it begins to roll off, ff , so it contains

signi cant energy at 1 GHz and above. Short rise time is so important because it is the

pulse's dV / dt as well as the dI / dt that it causes which allow ESD to induce currents and
voltages in a device's circuits which lead to failures. Suppose, for example, that a PCB
track within the medical device's circuit has an inductance of 10 nH/cm. If current from an
ESD event is directly or indirectly coupled to that PCB track, the voltage induced along a
length l of that track will be given by

fi

d
d

I
t

V 10(nH/cm) l (cm)

R S S

CHARGE CHARGE ESD

330

Device
Under
Test

150pF

High Voltage
DC Supply

Figure 4.18 The human body model of ESD represents discharge delivered to a device from the
fingertip of a standing person. It is modeled by a 150-pF capacitor discharged through a switching
component and a 330-Ω series resistor into the device under test.

TABLE 4.7 IEC-801-2 (1991) ESD Waveform Parameters

First Peak

Severity Voltage Current of Discharge Rise Time Current at Current at

Level (kV) ( 5%) (A) ( 10%) (ns) 30 ns (A) ( 30%) 60 ns (A) ( 30%)

1 2 7.5 0.7-1 4 2

2 4 15 0.7-1 8 4

3 6 22.5 0.7-1 12 6

4 8 30 0.7-1 16 8