SP3238E Datasheet, PDF (16/20 Pages) Sipex Corporation – Intelligent +3.0V to +5.5V RS-232 Transceivers

ESD TOLERANCE
The SP3238E device incorporates ruggedized
ESD cells on all driver output and receiver input
pins. The ESD structure is improved over our
previous family for more rugged applications
and environments sensitive to electro-static
discharges and associated transients. The
improved ESD tolerance is at least +15kV
without damage nor latch-up.
There are different methods of ESD testing
applied:
a) MIL-STD-883, Method 3015.7
b) IEC1000-4-2 Air-Discharge
c) IEC1000-4-2 Direct Contact
The Human Body Model has been the generally
accepted ESD testing method for semiconductors.
This method is also specified in MIL-STD-883,
Method 3015.7 for ESD testing. The premise of
this ESD test is to simulate the human body’s
potential to store electro-static energy and
discharge it to an integrated circuit. The
simulation is performed by using a test model as
shown in Figure 20. This method will test the
IC’s capability to withstand an ESD transient
during normal handling such as in manufacturing
areas where the ICs tend to be handled frequently.
The IEC-1000-4-2, formerly IEC801-2, is
generally used for testing ESD on equipment and
systems. For system manufacturers, they must
guarantee a certain amount of ESD protection
since the system itself is exposed to the outside
environment and human presence. The premise
with IEC1000-4-2 is that the system is required
to withstand an amount of static electricity when
ESD is applied to points and surfaces of the
equipment that are accessible to personnel during
normal usage. The transceiver IC receives most
of the ESD current when the ESD source is
applied to the connector pins. The test circuit for
IEC1000-4-2 is shown on Figure 21. There are
two methods within IEC1000-4-2, the Air
Discharge method and the Contact Discharge
method.
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.
RR_CC
RR_SS
DC Power
Source
SSWW11
C_SS
SSWW22
Device
Under
Test
Figure 20. ESD Test Circuit for Human Body Model
SP3238EDS/04
SP3238E +3.0V to +5.5V RS-232 Transceivers
16
© Copyright 1999 Sipex Corporation