SP3220EB datasheet(15/21 Pages) SIPEX

15 / 21 page

Date: 8/30/05

SP3220E/EB/EU High ESD RS-232 Driver/Receiver

Date: 8/22/05

SP3220E/EB/EU High ESD RS-232 Driver/Receiver

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

transfered without the air-gap arc. In situa-

tions such as hand held systems, the ESD

charge can be directly discharged to the

equipment from a person in contact with the

equipment. The current is transferred on to

the keypad or the serial port of the equip-

ment directly and then travels through the

PCB and finally to the IC.

The circuit models in Figure 20 and 21

represent the typical ESD testing circuits

used for all three methods. The C

S 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 ap-

plied through R

S, the current limiting resis-

tor, onto the device under test (DUT). In

ESD tests, the SW2 switch is pulsed so that

the device under test recives a duration of

voltage.

Figure 21. ESD Test Circuit for IEC1000-4-2

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

Contact-Discharge Module

SW1

SW2

Device

Under

Test

DC Power

Source

SW1

SW2

Contact-Discharge Module

For the Human Body Model, the current

limiting resistor (R

S) and the source capaci-

tor (C

S) are 1.5k

and 100pF, respectively.

For IEC-1000-4-2, the current limiting resis-

tor (RS) and the source capacitor (CS) are

330 and 150pF, respectively.

The higher CS value and lower RS value in

the IEC1000-4-2 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.

30A

15A

t=0nS

t=30nS

Figure 22. ESD Test Waveform for IEC1000-4-2

Device Pin

Human Body

IEC1000-4-2

Tested

Model

Air Discharge Direct Contact Level

Driver Ouputs

15kV

8kV

Receiver Inputs

15kV

8kV

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