SP3222EH_06 Datasheet, PDF (11/19 Pages) Sipex Corporation – 3.3V, 460 Kbps RS-232 Transceivers

Phase 4: V_DDTransfer (Figure 16)
The fourth phase of the clock connects the
negative terminal of C₂ to GND, and transfers
this positive generated voltage across C to C ,
2
4
the V_DD storage capacitor. This voltage is
regulated to +5.5V. At this voltage, the internal
oscillator is disabled. Simultaneous with the
transfer of the voltage to C₄, the positive side of
capacitor C is switched to V and the negative
1
CC
side is connected to GND, allowing the charge
pump cycle to repeat. The charge pump cycle
will continue as long as the operational
conditions for the internal oscillator are present.
Since both V⁺ and V^– are separately generated
from V_CC; in a no–load condition V⁺ and V^– will
be symmetrical. Older charge pump approaches
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 charge pump clock rate typically operates
at 250kHz. The external capacitors can be as low
as 0.1µF with a 16V breakdown voltage rating.
ESD Tolerance
The SP3222EH/3232EH series incorporates
ruggedized ESD cells on all driver output
and receiver input pins. The improved ESD
tolerance is at least ±15kV without damage or
latch-up.
Three methods of ESD testing are performed:
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. 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 17. 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
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. In many cases, the RS232
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 18. 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. The high
energy potential on the person discharges
through an arcing path to the rear panel of the
system before he or she 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.
Date: 1/18/06
SP3222EH/3232EH 3.3V, 460 Kbps RS-232 Transceivers
11
© Copyright 2006 Sipex Corporation