15

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

SP3070E-SP3078E_100_061109

ESD structures withstand high ESD in all

states: normal operation, shutdown, and

powered down. After an ESD event, the

SP3070E - SP3078E keep working without

latchup or damage.

ESDprotectioncanbetestedinvariousways.

Thetransmitteroutputsandreceiverinputsof

the SP3070E - SP3078E are characterized

for protection to the following limits:

■ ±15kV using the Human Body Model

■ ±8kVusingtheContactDischargemethod

specified in IEC 1000-4-2

■ ±15kV Airgap

ESD TEST CONDITIONS

ESD performance depends on a variety

of conditions. Contact Exar for a reliability

report that documents test setup, methodol-

ogy and results.

IEC 1000-4-2

The IEC 1000-4-2 standard covers ESD

testing and performance of finished equip-

ment. However, it does not specifically refer

to integrated circuits.The SP3070E family of

devices helps you design equipment to meet

IEC1000-4-2,withouttheneedforadditional

ESD-protection components.

The air-gap test involves approaching the

device with a charged probe. The contact-

discharge method connects the probe to the

device 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.

DETAILED DESCRIPTION

256 TRaNSCEIVERS ON THE BuS

The standard RS-485 receiver input imped-

ance is 12kΩ (1 unit load), and the standard

driver can drive up to 32 unit loads. The

SP3070E family of transceivers has a 1/8-

unit load receiver input impedance (96kΩ),

allowing up to 256 transceivers to be con-

nected in parallel on one communication

line. Any combination of these devices as

well as other RS-485 transceivers with a

total of 32 unit loads or fewer can be con-

nected to the line.

REDuCED EMI aND REFlECTIONS

The SP3070E, SP3071E and SP3072E

feature reduced slew-rate drivers that mini-

mize EMI and reduce reflections caused by

improperlyterminatedcables,allowingerror-

free data transmission up to 250kbps. The

SP3073E, SP3074E and SP3075E offer

higherdriveroutputslew-ratelimits,allowing

transmit speeds up to 500kbps.

lOW POWER SHuTDOWN MODE

Low-power shutdown mode is initiated by

bringing both RE high and DE low. In shut-

down, the devices typically draw only 50nA

of supply current.

RE and DE can be driven simultaneously;

the parts are guaranteed not to enter shut-

down 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 guaranteed to

enter shutdown.

Enable times t

not in a low-power shutdown state. Enable

times t

wereshutdown.Ittakesdriversandreceivers

longer to become enabled from low-power

shutdownmodet

driver/receiver-disable mode (t

DRIVER OuTPuT PROTECTION

Two mechanisms prevent excessive output

current and power dissipation caused by

faults or by bus contention. First, current

limit on the ouput stage, provides immedi-

ate protection against short circuits over the

whole common-mode voltage range.

The major difference between tests done

using the Human Body Model and IEC

1000-4-2 is higher peak current in IEC

1000-4-2, because series resistance is

lower in the IEC 1000-4-2 model. Hence,

the ESD withstand voltage measured to

EC 1000-4-2 is generally lower than that

measured using the human body model.