ADM3485E

–9–

REV. A

100%

90%

36.8%

10%

TIME

t

Figure 21. Human Body Model Current Waveform

Table IV. ESD Test Results

ESD Test Method

I-O Pins

IEC1000-4-2: Contact

±8 kV

TIME

t

100%

90%

10%

0.1 TO 1ns

30ns

60ns

Figure 22. IEC1000-4-2 ESD Current Waveform

FAST TRANSIENT BURST IMMUNITY (IEC1000-4-4)

IEC1000-4-4 (previously 801-4) covers electrical fast-transient/

burst (EFT) immunity. Electrical fast transients occur as a

result of arcing contacts in switches and relays. The tests simu-

late the interference generated when, for example, a power relay

disconnects an inductive load. A spark is generated due to the

well known back EMF effect. In fact, the spark consists of a

burst of sparks as the relay contacts separate. The voltage ap-

pearing on the line, therefore, consists of a burst of extremely

fast transient impulses. A similar effect occurs when switching

on fluorescent lights.

The fast transient burst test, defined in IEC1000-4-4, simulates

this arcing and its waveform is illustrated in Figure 23. It con-

sists of a burst of 2.5 kHz to 5 kHz transients repeating at

300 ms intervals. It is specified for both power and data lines.

Four severity levels are defined in terms of an open-circuit volt-

age as a function of installation environment. The installation

environments are defined as

1. Well-Protected

2. Protected

3. Typical Industrial

4. Severe Industrial

300ms

16ms

5ns

50ns

0.2/0.4ms

t

t

V

V

Figure 23. IEC1000-4-4 Fast Transient Waveform

Table V shows the peak voltages for each of the environments.

Table V. Peak Voltages

Level

1

0.5

0.25

2

1

0.5

32

1

44

2

A simplified circuit diagram of the actual EFT generator is

illustrated in Figure 24.

HIGH

VOLTAGE

SOURCE

L

50

OUTPUT

Figure 24. EFT Generator

These transients are coupled onto the signal lines using an EFT

coupling clamp. The clamp is 1 m long and completely sur-

rounds the cable, providing maximum coupling capacitance

(50 pF to 200 pF typ) between the clamp and the cable. High

energy transients are capacitively coupled onto the signal lines.

Fast rise times (5 ns) as specified by the standard result in very

effective coupling. This test is very severe since high voltages are

coupled onto the signal lines. The repetitive transients can often

cause problems, where single pulses do not. Destructive latchup

may be induced due to the high energy content of the transients.

Note that this stress is applied while the interface products are

powered up and are transmitting data. The EFT test applies

hundreds of pulses with higher energy than ESD. Worst case

transient current on an I-O line can be as high as 40 A.