SP2209E Datasheet, PDF(11/15 Page) Sipex Corporation – High ESD Dual Port RS-232 Transceiver

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SP2209E Datasheet, PDF (11/15 Pages) Sipex Corporation – High ESD Dual Port RS-232 Transceiver

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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

EN61000-4-2 is shown on Figure 11. There are

two methods within EN61000-4-2, 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

RRCC

SSWW11

DC Power

Source

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 10 and 11 represent

the typical ESD testing circuit used for all three

methods. The CS is initially charged 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. The

voltage stored in the capacitor is then applied

through RS, 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.

For the Human Body Model, the current limiting

resistor (R ) and the source capacitor (C ) are

1.5kâ¦ an 100pF, respectively. For EN61000-4-2,

the current limiting resistor (RS) and the source

capacitor

(C )

are

330â¦

150pF,

respectively.

The higher CS value and lower RS value in the

EN61000-4-2 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.

APPLICATIONS

With six drivers and ten receivers, the SP2209E

device is ideal for applications requiring two

RS-232 ports such as in desktop or portable

computers. Refer to Figure 13. For typical DB9

serial ports for Data Terminal Equipment (DTE)

RSS

SSWW22

CSS

Device

Under

Test

Figure 10. ESD Test Circuit for Human Body Model

SP2209E DS/06

SP2209E High ESD Dual Port RS-232 Transceivers

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