SP211EHE Datasheet, PDF (11/19 Pages) Exar Corporation – Low Power, High ESD 5V RS-232 Transceivers

R_C
DC Power
Source
SW1
Contact-Discharge Model
R_S
R_V
SW2
C_S
Device
Under
Test
RS and RV add up to 330Ω for IEC61000-4-2.
Figure 8. ESD Test Circuit for IEC61000-4-2
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 model in Figures 7 and 8 represent
the typical ESD testing circuit 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 sec-
ond switch (SW2) is on while SW1 switches
off. The voltage stored in the capacitor is
then applied through R_S, 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 dura-
tion of voltage.
For the Human Body Model, the current
limiting resistor (R_S) and the source capacitor
30A
15A
0A
t=0ns
t
t=30ns
Figure 9. ESD Test Waveform for IEC61000-4-2
(C_S) are 1.5kΩ an 100pF, respectively.For
IEC61000-4-2, the current limiting resistor
(R_S) and the source capacitor (C_S) are 330Ω
an 150pF, respectively.
The higher C_S value and lower R_S value in
the IEC61000-4-2 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.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
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