sp385e-1 Exar Corporation, sp385e-1 Datasheet - Page 8

• Manufacturer Part Number: sp385e-1
• Description: 232 Line Driver/receiver
• Manufacturer: Exar Corporation

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
Figure 8. ESD Test Waveform for IEC1000-4-2
Table 1. Transceiver ESD Tolerance Levels
SP385E-1
Family
Driver Outputs
Receiver Inputs
Rev. 07/26/02
30A
15A
0A
0ns
HUMAN BODY
MODEL
±15kV
±15kV
SP385E-1 True +3V to +5V RS-232 Line Driver/Receiver
30ns
Air Discharge
±15kV
±15kV
8
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
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
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
(C
IEC-1000-4-2, the current limiting resistor
(R
150pF, respectively.
The higher C
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.
S
S
S
, the current limiting resistor, onto the
) are 1.5k an 100pF, respectively. For
) and the source capacitor (C
Direct Contact
IEC1000-4-2
S
value and lower R
±8kV
±8kV
S
) and the source capacitor
© Copyright 2002 Sipex Corporation
S
is initially
S
) are 330 an
S
value in the
Level
4
4