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Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP3080E-SP3088E_100_062309

DESCRIPTION

the SP3080E - SP3088E are characterized for

protection to the following limits:

±15kV using the Human Body Model

±8kV using the Contact Discharge

method specified in IEC 1000-4-2

±15kV Air-gap

ESD TEST CONDITIONS

ESD performance depends on a variety of

conditions. Contact Exar for a reliability report

that documents test setup, methodology and

results.

IEC 1000-4-2

The IEC 1000-4-2 standard covers ESD testing

and performance of finished equipment. How-

ever, it does not specifically refer to integrated

circuits. The SP3080E family helps you design

equipment to meet IEC 1000-4-2, without sac-

rificing board space and cost for external ESD-

protection components.

The major difference between tests done us-

ing the Human Body Model and IEC 1000-4-2

is a higher peak current in IEC 1000-4-2 series

resistance is lower in the IEC 1000-4-2 model.

Hence, the ESD withstand voltage measured to

IEC 1000-4-2 is generally lower than that mea-

sured using the human body model.

The air-gap test involves approaching the de-

vice with a charged probe. The contact dis-

charge method connects the probe to the de-

vice before the probe is energized.

MACHINE MODEL

The machine model for ESD tests all pins using

a 200pF storage capacitor and zero discharge

resistance. The objective is to emulate the

stress caused when I/O pins are contacted by

handling equipment during test and assembly.

256 TRANSCEIVERS ON THE BUS

The standard RS-485 receiver input impedance

is 12kΩ (1 unit load). A standard driver can

drive up to 32 unit loads. The SP3080E fam-

ily of transceivers has only a 1/8th unit load re-

ceiver input impedance (96kΩ), thereby allow-

ing eight times as many, up to 256, transceivers

to be connected in parallel on a communication

line. Any combination of these devices and oth-

er RS-485 transceivers up to a total of 32 unit

loads may be connected to the line.

LOW POWER SHUTDOWN MODE

Low-power shutdown mode is initiated by bring-

ing both RE high and DE low simultaneously.

While in shutdown devices typically draw only

50nA of supply current. DE and RE may be tied

together and driven by a single control signal.

Devices are guaranteed not to enter shutdown

if RE is high and DE is low for less than 50ns. If

the inputs are in this state for at least 600ns, the

parts are shutdown.

not in low-power shutdown state. Enable times

are shut down. The drivers and receivers take

longer to become enabled from low power shut-

DRIVER OUTPUT PROTECTION

Two mechanisms prevent excessive output cur-

rent and power dissipation caused by faults or

by bus contention. First, a driver-current limit

on the output stage provides immediate protec-

tion against short circuits over the whole com-

mon-mode voltage range. Second, a thermal-

shutdown circuit forces the driver outputs into

a high-impedance state if junction temperature

becomes excessive.

LINE LENGTH, EMI, AND REFLECTIONS

SP3080E - SP3085E feature controlled slew-

rate drivers that minimize EMI and reduce reflec-

tions caused by improperly terminated cables.

SP3080E - SP3083E driver rise and fall times

are limited to no faster than 667ns, allowing er-

ror-free data transmission up to 115kbps. The

SP3083, SP3084 and SP3085 offer somewhat

higher driver output slew-rate limits, allowing

transmit speeds up to 500kbps.

The RS-485/RS-422 standard covers line

lengths up to 4,000ft. Maximum achievable

line length is a function of signal attenuation

and noise. Use of slew-controlled drivers such

as the SP3080E-SP3086E may help to reduce

crosstalk interference and permit communica-

tion over longer transmission lines.