Zywyn Corporation
ZT4xxE
CircuitDescription
Bus Configuration
The ZT483E, ZT485E, ZT489E, ZT490E, and ZT491E are
low-powertransceiversforRS-485andRS-422communica-
tions. The RS-485 standard is ideal for multi-drop applica-
tions and for long-distance interfaces. The TIA/EIA-485
specification allows up to 32 drivers and 32 receivers to be
connected to a data bus, making it an ideal choice for multi-
drop applications. RS-485 transceivers are equipped with a
wide (-7V to +12V) common mode range to accommodate
ground potential differences since the cabling can be as
longas4,000feet. AsRS-485isadifferentialinterface, data
is virtually immune to noise in the transmission line.
TheZT489E,ZT490E,andZT491Earefull-duplextransceiv-
ers, while the ZT483E and ZT485E are half-duplex.
For full duplex, the devices are used as a four-wire bus
transceiver with a configuration that the transmitters and
receiversaremovingdataindependentofeachother. Trans-
mit can occur on a dedicated two-wire pair and receive can
occur on an adjacent two-wire pair, with each pair transfer-
ring data at up to 10Mbps (up to 250kbps for the ZT489E).
Half duplex is a configuration where the transmitter outputs
are connected to its receiver inputs. This application is
commonfortwo-wireinterfaceswhereeitherthetransmitter
is active or the receiver is active. It is common to connect
theenableinputsforthetransmitterandreceivertogetherso
that a logic HIGH will enable the transmitter and disable the
receiver. Conversely, a logic LOW will disable the transmit-
ter and enable the transmitter. Half-duplex configuraitons
and these devices are designed for bidirectional data trans-
mission on multipoint twisted-pair cables for applications,
such as digital motor controllers, remote sensors and
terminals, industrial process control, security stations and
environmental control systems.
The ZT483E, ZT488E, and ZT489E are slew-rate limited,
minimizing EMI and reducing reflections caused by improp-
erly terminated cables.
RS-485 Transmitters
Each device in the ZT4xxE family contains a differential
output line transmitter that can drive voltage into multiple
loads on a terminated two-wire pair, and a receiver that
accepts a differential voltage down to 200mV. The
transmitter'sdifferentialoutputcancomplywithRS-485and
also RS-422 standards. The typical voltage output swing
with no load is 0V to V . With worst case loading of 54
CC
ohms across the differential outputs, the drivers can main-
tain greater than 1.5V voltage levels, which is more than
adequate for a differential receiver to acknowledge a logic
state. The 54 ohms is the equivalent of two 120 ohm
termination resistors placed on each side of the transmis-
sionlineandtheinputimpedanceof32receiversontheline.
ESD Immunity
Electro-Static Discharge (ESD) is an important factor when
implementing a serial port into a system, especially in harsh
environmental conditions. These industrial strength de-
vicesprovideextraprotectionagainstESDandareintended
forharshenvironmentswherehigh-speeddatacommunica-
tion is important.
The ZT485E transmitter has an enable control line which is
active HIGH. A logic HIGH on DE (pin 3) will enable the
differential outputs. A logic LOW on DE (pin 3) will disable
the transmitter outputs. While disabled, the transmitter
outputs are in high impedance.
All of the ZT485E family of transceivers incorporate internal
protection structures on all pins to protect against ESD
charges encountered during handling and assembly. The
driver outputs and receiver inputs have extra protection
against static electricity as they are directly interfacing to
the outside environment. As such, these pins against ESD
of ±15kV without damage in all states of the transceiver's
operation in the static state. After multiple ESD events,
Zywyn’sZT485Efamilyoftransceiverskeepworkingwithout
latchup. These devices eliminate the need for external
transient suppressor diodes and the associated high ca-
pacitance loading, allowing reliable high-speed data com-
munications.
RS-485 Receivers
Each transceiver contains one differential receiver that has
an input sensitivity of 200mV. The input impedance of the
receivers is typically 15 kohms. A wide common mode
range of -7V to +12V allows for large ground potential
differences between systems.
TheZT485E,ZT489E,andZT491Ereceivershaveanenable
control input. A logic LOW on RE will enable the receiver,
a logic HIGH on RE will disable the receiver. The receivers
are equipped with the fail-safe feature, which guarantees
thatthereceiveroutputwillbeinaHIGH-IMPEDANCEstate
when the input is left unconnected.
The Human Body Model has been the generally accepted
ESD testing method for semiconductors. This test is in-
tended to simulate the human body’s potential to store
electrostatic energy and discharge it to an integrated circuit
upon close proximity or contact. This method will test the
IC’s capability to withstand an ESD transient during normal
handlingsuchasinmanufacturingareaswheretheICstend
to be handled frequently.
TheZT485E,ZT490E,andZT491Ecantransmitandreceive
at data rates up to 10Mbps. The ZT483E, ZT488E, and
ZT489E are specified for data rates up to 250kbps.
Specifications subject to change without notice
Zywyn
7
August 2004
rev.1.2