SP485EN-L Datasheet, PDF (8/11 Pages) Exar Corporation – Low Power Half-Duplex RS-485 Transceivers

The SP483 and SP485 are half-duplex dif-
ferential 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
SP483 and SP485
The driver outputs of the SP483 and SP485
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 voltage levels.
The drivers of the SP483 and SP485 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 SP485 will operate up
to at least 5Mbps. The SP483 has internally
slew rate limited driver outputs to minimize
EMI. The maximum data rate for the SP483
driver is 250kbps.
Receivers
SP483 and SP485
DESCRIPTION
The SP483 and SP485 receivers have dif-
ferential 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
SP483 and SP485 have a tri-state enable
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 SP485 will operate up
to at least 10Mbps. The SP483 receiver
is rated for data rates up to 250kbps. The
receiver for each of the three 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 and floating.
Shutdown Mode
SP483
The SP483 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 SP483
into Shutdown mode. In Shutdown, supply
current will drop to typically 1µA.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

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