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SP48E-485E_00_06609

8

With the Air Discharge Method, an ESD

voltageisappliedtotheequipmentunder

test(EUT)throughair.Thissimulatesan

electricallychargedpersonreadytoconnect

acableontotherearofthesystemonlyto

findanunpleasantzapjustbeforetheperson

touchesthebackpanel.Thehighenergy

potentialonthepersondischargesthrough

anarcingpathtotherearpanelofthesystem

beforeheorsheeventouchesthesystem.

Thisenergy,whetherdischargeddirectlyor

throughair,ispredominantlyafunctionofthe

dischargecurrentratherthanthedischarge

voltage.Variableswithanairdischargesuch

asapproachspeedoftheobjectcarryingthe

ESDpotentialtothesystemandhumidity

willtendtochangethedischargecurrent.

Forexample,therisetimeofthedischarge

currentvarieswiththeapproachspeed.

TheContactDischargeMethodappliesthe

ESDcurrentdirectlytotheEUT.Thismethod

wasdevisedtoreducetheunpredictability

oftheESDarc.Thedischargecurrentrise

timeisconstantsincetheenergyisdirectly

transferredwithouttheair-gaparc.Insitu-

ationssuchashandheldsystems,theESD

charge can be directly discharged to the

equipment from a person already holding

theequipment.Thecurrentistransferred

ontothekeypadortheserialportofthe

equipmentdirectlyandthentravelsthrough

thePCBandfinallytotheIC.

ThecircuitmodelinFigures7and8represent

thetypicalESDtestingcircuitusedforall

threemethods.TheC

with the DC power supply when the first

switch(SW1)ison.Nowthatthecapacitor

ischarged,thesecondswitch(SW2)ison

whileSW1switchesoff.Thevoltagestored

inthecapacitoristhenappliedthroughR

thecurrentlimitingresistor,ontothedevice

undertest(DUT).InESDtests,theSW2

switchispulsedsothatthedeviceunder

testreceivesadurationofvoltage.

For the Human Body Model, the current

limitingresistor(R

(C

IEC-1000-4-2, the current limiting resistor

(R

an150pF,respectively.

ThehigherC

theIEC1000-4-2modelaremorestringent

thantheHumanBodyModel.Thelarger

storage capacitor injects a higher voltage

tothetestpointwhenSW2isswitchedon.

Thelowercurrentlimitingresistorincreases

thecurrentchargeontothetestpoint.

Figure9.ESDTestWaveformforIEC1000-4-2

t=0ns

t=30ns

0A

5A

30A

t

HUMAn BodY

iec1000-4-2

ModeL

Air discharge

direct contact

Level

DriverOutputs ±15kV

±15kV

±8kV

4

ReceiverInputs ±15kV

±15kV±8kV

4

SP1481E,

SP1485E

FamiLy