SP3222 datasheet(13/19 Pages) SIPEX

13 / 19 page

Date: 06/22/04

SP3222EH/3232EH 3.3V, 460 Kbps RS-232 Transceivers

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.

The circuit models in Figures 17 and 18

represent the typical ESD testing circuits 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.

SW1

SW2

Device

Under

Test

DC Power

Source

SW1

SW2

Figure 17. ESD Test Circuit for Human Body Model

S and

and R

V add up to 330

add up to 330Ω

Ω ffor IEC1000-4-2.

or IEC1000-4-2.

RS and RV add up to 330Ω for IEC1000-4-2.

Contact-Discharge Module

RVV

CSS

RSS

SW1

SW2

Device

Under

Test

DC Power

Source

SW1

SW2

Contact-Discharge Module

Figure 18. ESD Test Circuit for IEC1000-4-2

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