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

SP490E,49E_00_0527

ESDTOLERANCE

The SP490E/SP49E devices incorporates

ruggedized ESD cells on all driver output

and receiver input pins. The ESD structure

is improved over our previous family for

more rugged applications and environments

sensitive to electro-static discharges and

associated transients. The improved ESD

tolerance is at least ±5kV without damage

nor latch-up.

There are different methods of ESD testing

applied:

a) MIL-STD-883, Method 305.7

b) IEC6000-4-2 Air-Discharge

c) IEC6000-4-2 Direct Contact

The Human Body Model has been the

generally accepted ESD testing method

for semiconductors. This method is also

specified in MIL-STD-883, Method 3015.7

for ESD testing.The premise of this ESD test

is to simulate the human body’s potential to

store electro-static energy and discharge it

to an integrated circuit. The simulation is

performed by using a test model as shown

in Figure 9. This method will test the IC’s

capability to withstand an ESD transient

during normal handling such as in manu-

facturing areas where the ICs tend to be

handled frequently.

The IEC-6000-4-2, formerly IEC80-2, is

generallyusedfortestingESDonequipment

and systems. For system manufacturers,

theymustguaranteeacertainamountofESD

protection since the system itself is exposed

to the outside environment and human pres-

ence. ThepremisewithIEC6000-4-2isthat

thesystemisrequiredtowithstandanamount

of static electricity when ESD is applied to

points and surfaces of the equipment that

are accessible to personnel during normal

usage. The transceiver IC receives most

of the ESD current when the ESD source is

appliedtotheconnectorpins. Thetestcircuit

for IEC6000-4-2 is shown on Figure 0.

TherearetwomethodswithinIEC6000-4-2,

the Air Discharge method and the Contact

Discharge method.

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 0 repre-

sent the typical ESD testing circuit used for

all three methods. The C

with the DC power supply when the first

switch (SW) is on. Now that the capacitor

is charged, the second switch (SW2) is on

while SW switches off. The voltage stored

in the capacitor is then applied through R

the current limiting resistor, onto the device

under test (DUT). In ESD tests, the SW2

switch is pulsed so that the device under

test receives a duration of voltage.