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Exar Corporation 48720 Kato Road, Fremont CA, 94538 50-668-707 www.exar.com
SP3483_00_0092
The
SP3483 device is part of a family of
+3.3V low power half-duplex transceivers
that meet the specifications of the RS-485
and RS-422 serial protocols. This device is
pin-to-pin compatible with the
Exar SP483
deviceaswellaspopularindustrystandards.
The
SP3483 features Exar's BiCMOS pro-
cess allowing low power operation without
sacrificing performance.
The RS-485 standard is ideal for multi-drop
applicationsandforlong-distanceinterfaces.
RS-485allowsupto32driversand32receiv-
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 +2V) 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
SP3483 are dif-
ferential outputs meeting the RS-485 and
RS-422 standards. The typical voltage
output swing with no load will be 0 Volts to
+3.3 Volts. With worst case loading of 54
across the differential outputs, the drivers
can maintain greater than .5V voltage
levels. The drivers 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
force the driver outputs into high impedance
(high-Z).
The
SP3483 has internally slew rate lim-
ited driver outputs to minimize EMI. The
transceivers will operate up to 250kbps.
The 250mA I
SC maximum limit on the driver
output allows the
SP3483 to withstand an
infinite short circuit over the -7.0V to +12V
common mode range without catastrophic
damage to the IC.
Receivers
The
SP3483 receiver has differential inputs
with an input sensitivity as low as ±200mV.
Input impedance of the receivers is typically
15k (12k minimum). A wide common
mode range of -7V to +2V allows for large
ground potential differences between sys-
tems. The receiver of the
SP3483 has a tri-
state enable control input RE (Pin 2). A logic
LOW on RE will enable the receiver, a logic
HIGH on RE will disable the receiver.
The receiver of the
SP3483 will operate
up to 250kbps. The receiver is equipped
with the fail-safe feature. Fail-safe guar-
antees that the receiver output will be in a
HIGH state when the input is left uncon-
nected (open circuit).
Shutdown Mode
The
SP3483 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
SP3483 into Shutdown mode. In Shutdown,
supply current will drop to typically A,
0A maximum.
DESCRIPTION