SP3282 Datasheet, PDF (11/15 Pages) Sipex Corporation – Intelligent +2.35V to +5.5V RS-232 Transceivers

external transmitters are disabled. Otherwise,
R_XINACT will be at a logic LOW. This circuit is
duplicated for each of the other receivers.
The second stage of the AUTO ON-LINE^® cir-
cuitry, shown in Figure 16, processes all the
receiver's R_XINACT signals with an accumulated
delay that disables the device to a 1µA supply
current. The STATUS pin goes to a logic LOW
when the cable is disconnected, or when the exter-
nal transmitters are disabled.
When the drivers or internal charge pump are
disabled, the supply current is reduced to 1µA.
This can commonly occur in hand-held or
portable applications where the RS-232 cable is
disconnected or the RS-232 drivers of the
connected peripheral are turned off.
The AUTO ON-LINE^® mode can be disabled by
the SHUTDOWN pin. If this pin is a logic LOW,
the AUTO ON-LINE^® function will not operate
regardless of the logic state of the ONLINE pin.
Table 3 summarizes the logic of the AUTO ON-
LINE^® operating modes and the truth table logic of
the driver and receiver outputs.
When the SP3282EB device is shut down, the
charge pump is turned off. V+ charge pump output
decays to V_CC, the V- output decays to GND. The
decay time will depend on the size of capacitors
used for the charge pump. Once in shutdown, the
time required to exit the shut down state and have
valid V+ and V- levels is typically 200µs.
For easy programming, the STATUS pin can be
used to indicate DTR or a Ring Indicator signal.
Tying ONLINE and SHUTDOWN together
will bypass the AUTO ON-LINE^® circuitry so this
connection acts like a shutdown input pin.
ESD TOLERANCE
The SP3282EB 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 tol-
erance is at least +15kV without damage nor latch-
up.
There are different methods of ESD testing ap-
plied:
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 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.
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
Date: 02/24/05
SP3282EB Intelligent +2.35V to +5.5V RS-232 Transceivers
11
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