SP385E-1 Datasheet, PDF (8/11 Pages) Sipex Corporation – True +3V or +5V RS-232 Line Driver/Receiver

30A
15A
0A
0ns
30ns
Figure 8. ESD Test Waveform for IEC1000-4-2
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.
The circuit models in Figures 6 and 7
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 second 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 duration of voltage.
For the Human Body Model, the current
limiting resistor (R ) and the source capacitor
S
(C_S) are 1.5kΩ an 100pF, respectively. For
IEC-1000-4-2, 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
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.
SP385E-1
Family
HUMAN BODY
IEC1000-4-2
MODEL
Air Discharge Direct Contact
Driver Outputs
Receiver Inputs
±15kV
±15kV
±15kV
±15kV
±8kV
±8kV
Table 1. Transceiver ESD Tolerance Levels
Level
4
4
Rev. 07/26/02
SP385E-1 True +3V to +5V RS-232 Line Driver/Receiver
8
© Copyright 2002 Sipex Corporation