This voltage is regulated to +5.5V. At this
voltage, the internal oscillator is disabled. Si-
multaneous with the transfer of the voltage to
C4, the positive side of capacitor C1 is switched
to VCC and the negative side is connected to
GND, allowing the charge pump cycle to begin
again. The charge pump cycle will continue as
long as the operational conditions for the inter-
nal oscillator are present.
The simulation is performed by using a test
model as shown in Figure 18. 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 19. There are two methods
within IEC1000-4-2, the Air Discharge method
and the Contact Discharge method.
Since both V+ and V– are separately generated
from VCC; in a no–load condition V+ and V– will
besymmetrical. Olderchargepumpapproaches
that generate V– from V+ will show a decrease in
the magnitude of V– compared to V+ due to the
inherent inefficiencies in the design.
The clock rate for the charge pump typically
operatesat250kHz. Theexternalcapacitorscan
be as low as 0.1µF with a 16V breakdown
voltage rating.
ESD Tolerance
The SP3222EB/3232EB series 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 electrostatic discharges and associated
transients. The improved ESD tolerance is at
least ±15kV without damage nor latch-up.
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.
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 semiconduc-
tors. ThismethodisalsospecifiedinMIL-STD-
883,Method3015.7forESDtesting.Thepremise
of this ESD test is to simulate the human body’s
potential to store electrostatic energy and
discharge it to an integrated circuit.
Rev. A Date:12/11/03
SP3222EB/3232EB True +3.0 to +5.5V RS-232 Transceivers
© Copyright 2003 Sipex Corporation
11
SIPEX [ SIPEX CORPORATION ]
