11

Rev. 6/19/03

SP3281EB Intelligent +2.35V to +5.5V RS-232 Transceivers

© Copyright 2003 Sipex Corporation

external transmitters are disabled. Otherwise,

R

duplicated for each of the other receivers.

cuitry, shown in Figure 16, processes all the

receiver's R

delay that disables the device to a 1

µA 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 1

µA.

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 SHUTDOWN pin. If this pin is a logic LOW,

regardless of the logic state of the ONLINE pin.

Table 3 summarizes the logic of the AUTO ON-

the driver and receiver outputs.

When the SP3281EB device is shut down, the

charge pump is turned off. V+ charge pump output

decays to V

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 200

µs.

For easy programming, the STATUS pin can be

used to indicate DTR or a Ring Indicator signal.

Tying ONLINE and SHUTDOWN together

connection acts like a shutdown input pin.

ESD TOLERANCE

The SP3281EB 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.

TheIEC-1000-4-2,formerlyIEC801-2,isgenerally

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