SP3243ECT datasheet(18/24 Pages) SIPEX

18 / 24 page

Rev. 11/14/02

SP3223E +3.0V to +5.5V RS-232 Transceivers

ESD TOLERANCE

The SP3223E/3243E series 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 +15kV without damage nor latch-up.

There are different methods of ESD testing

applied:

a) MIL-STD-883, Method 3015.7

b) IEC1000-4-2 Air-Discharge

c) IEC1000-4-2 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 25. This method will test the

IC’s capability to withstand an ESD transient

during normal handling such as in manufacturing

areas where the ICs tend to be handled frequently.

The IEC-1000-4-2, formerly IEC801-2, is

generally 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 IEC1000-4-2 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 during

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

IEC1000-4-2 is shown on Figure 26. There are

two methods within IEC1000-4-2, 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 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 system.

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 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.

SW1

SW2

Device

Under

Test

DC Power

Source

SW1

SW2

Figure 25. ESD Test Circuit for Human Body Model

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