SP1486E Datasheet, PDF (13/15 Pages) Sipex Corporation – +5V, 20Mbps PROFIBUS RS485/RS422 Transceivers Advanced Failsafe, 1/8th Unit Load, ±15kV ESD-Protected

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 SP1486E helps you design equip-
ment to meet IEC 1000-4-2, without sacrificing
board-space and cost for external ESD-protec-
tion components.
The major difference between tests done using
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
EC 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 RS485 receiver input impedance
is 12kΩ (1 unit load). A standard driver can
drive up to 32 unit loads. The SP1486E has
only a 1/8th unit load receiver input impedance
(96kΩ), thereby allowing eight times as many,
up to 256, transceivers to be connected in par-
allel on a communication line. Any combination
of these devices and other RS485 transceivers
up to a total of 32 unit loads may be connected
to the line.
DESCRIPTION
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 shut-down.
Enable times tzh and tzl apply when the part is
not in low-power shutdown state. Enable times
tzh(shdn) and tzl(shdn) apply when the parts
are shut down. The drivers and receivers take
longer to become enabled from low-power shut-
down mode tzh(shdn) and tzl(shdn) than from
driver/receiver-disable mode (tzh, tzl).
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.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
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