DESCRIPTION
The
SP481E
and
SP485E
are half-duplex
differential transceivers that meet the require-
ments of RS-485 and RS-422. Fabricated
with an
Exar
proprietary BiCMOS process,
this product requires a fraction of the power
of older bipolar designs.
The RS-485 standard is ideal for multi-drop
applications and for long-distance interfaces.
RS-485 allows up to 32 drivers and 32 receiv-
ers to be connected to a data bus, making it
an ideal choice for multi-drop applications.
Since the cabling can be as long as 4,000
feet, RS-485 transceivers are equipped with
a wide (-7V to +12V) common mode range
to accommodate ground potential differ-
ences. Because RS-485 is a differential
interface, data is virtually immune to noise
in the transmission line.
Drivers
The driver outputs of the
SP481E
and
SP485E
are differential outputs meeting the
RS-485 and RS-422 standards. The typical
voltage output swing with no load will be 0
Volts to +5 Volts. With worst case loading
of 54Ω across the differential outputs, the
drivers can maintain greater than 1.5V volt-
age levels. The drivers of the
SP481E
and
SP485E
have an enable control line which
is active HIGH. A logic HIGH on DE (pin 3)
will enable the differential driver outputs. A
logic LOW on the DE(pin 3) will tri-state the
driver outputs.
The transmitters of the
SP481E
and
SP485E
will operate up to at least 10Mbps.
Receivers
The
SP481E
and
SP485E
receivers have
differential inputs with an input sensitivity
as low as ±200mV. Input impedance of the
receivers is typically 15kΩ (12kΩ minimum).
A wide common mode range of -7V to +12V
allows for large ground potential differences
between systems. The receivers of the
SP481E
and
SP485E
have a tri-state en-
able control pin. A logic LOW on RE (pin 2)
will enable the receiver, a logic HIGH on RE
(pin 2) will disable the receiver.
The receiver for the
SP481E
and
SP485E
will operate up to at least 10Mbps. The
receiver for each of the two devices is
equipped with the fail-safe feature. Fail-
safe guarantees that the receiver output
will be in a HIGH state when the input is
left unconnected.
Shutdown Mode
SP481E
The
SP481E
is equipped with a Shutdown
mode. TO enable the shutdown state, both
driver and receiver must be disabled simul-
taneously. A logic LOW on DE (pin 3) and a
Logic HIGH on RE (pin 2) will put the
SP481E
into Shutdown mode. In Shutdown, supply
current will drop to typically µA.
ESD TOLERANCE
The
SP481E
and
SP485E
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
tolerance is at least ±15kV without damage
or latch-up.
There are different methods of ESD testing
applied:
a) MIL-STD-883, Method 305.7
b) IEC1000-4-2 Air-Discharge
c) IEC000-4-2 Direct Contact
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com
SP48E,485E_00_2808
7
EXAR [ EXAR CORPORATION ]
