sp3222eucy-tr Exar Corporation, sp3222eucy-tr Datasheet - Page 11

• Manufacturer Part Number: sp3222eucy-tr
• Description: Sp3232eh -3.3v, 460kbps Rs-232 Transceivers
• Manufacturer: Exar Corporation

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 internal oscillator are
present.
Since both V
from V
will be symmetrical. Older charge pump
approaches that generate V
show a decrease in the magnitude of V
compared to V
cies in the design.
The clock rate for the charge pump typically
operates at 250kHz. The external capacitors
can be as low as 0.1µF with a 16V breakdown
voltage rating.
ESD Tolerance
The SP3222EU/3232EU 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.
There are different methods of ESD testing
applied:
The Human Body Model has been the
generally accepted ESD testing method for
semiconductors. This method is also speci-
fied 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 electrostatic 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
Date: 02/31/06
CC
a) MIL-STD-883, Method 3015.7
b) IEC1000-4-2 Air-Discharge
c) IEC1000-4-2 Direct Contact
; in a no–load condition V
+
and V
+
due to the inherent inefficien-
–
are separately generated
SP3222EU, SP3232EU 3.3V, 1000Kbps RS-232 Transceivers
–
from V
+
+
and V
will
–
–
11
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 Dis-
charge 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 DUT.
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