SP211EHE Datasheet, PDF (10/19 Pages) Exar Corporation – Low Power, High ESD 5V RS-232 Transceivers

ESD Tolerance
The SP207E Family incorporates rug-
gedized ESD cells on all driver output
and receiver input pins. The ESD struc-
ture is improved over our previous fam-
ily 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) IEC61000-4-2 Air-Discharge
c) IEC61000-4-2 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 7. This method will test the IC’s
capability to withstand an ESD transient
during normal handling such as in manu-
facturing areas where the ICs tend to be
handled frequently.
The IEC-61000-4-2, 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 pres-
ence. The premise with IEC61000-4-2 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 IEC61000-4-2 is shown on Figure 8.
There are two methods within IEC61000-4-2,
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.
R_C
R_S
DC Power
Source
SW1
C_S
SW2
Device
Under
Test
Figure 7. ESD Test Circuit for Human Body Model
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
10
SP207E_101_101512