9

Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com

SP483E_00_02092

With the Air Discharge Method, an ESD

voltage is applied to the equipment under

test (EUT) through air. This simulates an

electrically charged person ready to connect

a cable onto the rear of the system only to

findanunpleasantzapjustbeforetheperson

touches the back panel. The high energy

potential on the person discharges through

an arcing path to the rear panel of the system

before he or she even touches the system.

This energy, whether discharged directly or

throughair,ispredominantlyafunctionofthe

discharge current rather than the discharge

voltage. Variableswithanairdischargesuch

as approach speed of the object carrying the

ESD potential to the system and humidity

will tend to change the discharge current.

For example, the rise time of the discharge

current varies with the approach speed.

The Contact Discharge Method applies the

ESDcurrentdirectlytotheEUT. Thismethod

was devised to reduce the unpredictability

of the ESD arc. The discharge current rise

time is constant since the energy is directly

transferred without the air-gap arc. In situ-

ations such as hand held systems, the ESD

charge can be directly discharged to the

equipment from a person already holding

the equipment. The current is transferred

on to the keypad or the serial port of the

equipment directly and then travels through

the PCB and finally to the IC.

The circuit model in Figures 9 and 10 repre-

sent the typical ESD testing circuit used for

all three methods. The C

with the DC power supply when the first

switch (SW1) is on. Now that the capacitor

is charged, the second switch (SW2) is on

while SW1 switches off.

t = 0ns

t = 30ns

0A

15A

30A

t →

Figure 11. ESD Test Waveform for IEC61000-4-2

The voltage stored in the capacitor is then

applied through R

resistor, onto the device under test (DUT).

In ESD tests, the SW2 switch is pulsed so

that the device under test receives a dura-

tion of voltage.

For the Human Body Model, the current

limitingresistor(R

(C

IEC-61000-4-2, the current limiting resistor

(R

an 150pF, respectively.

The higher C

the IEC61000-4-2 model are more stringent

than the Human Body Model. The larger

storage capacitor injects a higher voltage

to the test point when SW2 is switched on.

The lower current limiting resistor increases

the current charge onto the test point.

DEVICE PIN

TESTED

HUMAN BODY

MODEL

IEC6000-4-2

Air Discharge Direct Contact Level

Driver Outputs

Receiver Inputs

+/-5kV

+/-5kV

+/-5kV

+/-5kV

+/-8kV

+/-8kV

4

4

Table 1. Transceiver ESD Tolerance levels