DESCRIPTION
fail-safe feature. Fail-safe guarantees that the
receiver output will be in a HIGH state when
the input is left unconnected.
The SP1485E is half-duplex differential trans-
ceivers that meet the requirements of RS-485
andRS-422. FabricatedwithaSipexproprietary
BiCMOS process, this product requires a frac-
tion of the power of older bipolar designs.
ESD TOLERANCE
The SP1485E incorporates ruggedized ESD
cells on all driver output and receiver input pins.
The ESD structure is improved over our previ-
ous family for more rugged applications and
environments sensitive to electro-static dis-
chargesandassociatedtransients. Theimproved
ESD tolerance is at least ±15kV without damage
or latch-up.
The RS-485 standard is ideal for multi-drop
applications and for long-distance interfaces.
RS-485 allows up to 32 drivers and 32 receivers
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
groundpotentialdifferences. BecauseRS-485is
a differential interface, data is virtually immune
to noise in the transmission line.
There are different methods of ESD testing
applied:
a) MIL-STD-883, Method 3015.7
b) IEC1000-4-2 Air-Discharge
c) IEC1000-4-2 Direct Contact
Drivers
The Human Body Model has been the generally
acceptedESDtestingmethodforsemiconductors.
This method is also specified in MIL-STD-883,
Method 3015.7 for ESD testing. The premise of
this ESD test is to simulate the human body’s
potential to store electro-static energy and
discharge it to an integrated circuit. The
simulation is performed by using a test model as
shown in Figure 7. This method will test the
IC’s capability to withstand an ESD transient
duringnormalhandlingsuchasinmanufacturing
areaswheretheICstendtobehandledfrequently.
The driver outputs of the SP1485E are differen-
tial outputs meeting the RS-485 and RS-422
standards. Thetypicalvoltageoutputswingwith
no load will be 0 Volts to +5 Volts. With worst
case loading of 54Ω across the differential out-
puts, the drivers can maintain greater than 1.5V
voltage levels. The drivers of the SP1485E have
an enable control line which is active HIGH. A
logic HIGH on DE (pin 3) will enable the differ-
ential driver outputs. A logic LOW on DE (pin
3) will tri-state the driver outputs.
The transmitters of the SP1485E will operate up
to at least 20Mbps.
The IEC-1000-4-2, formerly IEC801-2, is
generallyusedfortestingESDonequipmentand
systems. For system manufacturers, they must
guarantee a certain amount of ESD protection
since the system itself is exposed to the outside
environment and human presence. The premise
with IEC1000-4-2 is that the system is required
to withstand an amount of static electricity when
ESD is applied to points and surfaces of the
equipmentthatareaccessibletopersonnelduring
normal usage. The transceiver IC receives most
of the ESD current when the ESD source is
applied to the connector pins. The test circuit for
Receivers
The SP1485E 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 re-
ceivers of the SP1485E 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 SP1485E will operate up to
atleast20Mbps. Thereceiverforeachofthe two
devices
is
equipped
with
the
Rev:C Date: 02/26/04
SP1485E Low Power Half-Duplex RS485 Transceivers
© Copyright 2004 Sipex Corporation
6
SIPEX [ SIPEX CORPORATION ]
