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Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP385E_100_030811

ESD TOLERANCE

The SP385E device 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 dis-

chargesandassociatedtransients.Theimproved

ESD tolerance is at least +15kV without damage

nor latch-up.

There are different methods of ESD testing ap-

plied:

a) MIL-STD-883, Method 3015.7

b) IEC61000-4-2 Air-Discharge

c) IEC61000-4-2 Direct Contact

The Human Body Model has been the generally

accepted ESD testing method for semi-con-

ductors. 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 6. This method will

test the IC’s capability to withstand an ESD

transient during normal handling such as in

manufacturing areas where the IC's tend to be

handled frequently.

The IEC-61000-4-2, formerly IEC801-2, is gen-

erally used for testing ESD on equipment and

systems. For system manufacturers, they must

guarantee a certain amount of ESD protection

since the system itself is exposed to the outside

environment and human presence. The premise

with IEC61000-4-2 is that the system is required

to withstand an amount of static electricity when

ESD is applied to points and surfaces of the

equipment that are accessible to personnel dur-

ing normal usage. The transceiver IC receives

most of the ESD current when the ESD source

is applied to the connector pins. The test circuit

for IEC61000-4-2 is shown on Figure 7. There

are two methods within IEC61000-4-2, 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)

throughair. Thissimulatesanelectricallycharged

person ready to connect a cable onto the rear of

the system only to find an unpleasant zap just

before the person 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 sys-

tem. This energy, whether discharged directly

or through air, is predominantly a function of

the discharge current rather than the discharge

voltage. Variables with an air discharge such 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 ESD

current directly to the EUT. This method 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 situations such as hand held sys-

tems, 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.

Figure 6. ESD Test Circuit for Human Body Model

Device

Under

Test

DC Power

Source

SW1

SW2