Zywyn Corporation
ZT4xxER
CircuitDescription
Bus Configuration
TheZT487E,ZT485ER,ZT489ER,ZT490ER,andZT491ER
arelow-powertransceiversforRS-485andRS-422commu-
nications. The RS-485 standard is ideal for multi-drop
applications 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 accom-
modate ground potential differences since the cabling can
be as long as 4,000 feet. As RS-485 is a differential
interface, data is virtually immune to noise in the transmis-
sion line.
TheZT489ER,ZT490ER,andZT491ERarefull-duplextrans-
ceivers, while the ZT487E and ZT485ER 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 ZT489ER).
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.
TheZT487E, ZT488ER, andZT489ERareslew-ratelimited,
minimizing EMI and reducing reflections caused by improp-
erly terminated cables.
RS-485 Transmitters
Each device in the ZT4xxER 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
ESD Immunity
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-
sion line and the input impedance of 128 receivers on the
line. The ZT485ER 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 trans-
mitter outputs are in high impedance.
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.
All of the ZT485ER family of transceivers incorporate inter-
nal 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’s ZT485ER family of transceivers keep working
without latchup. These devices eliminate the need for
external transient suppressor diodes and the associated
highcapacitanceloading, allowingreliablehigh-speeddata
communications.
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.
The ZT485ER, ZT489ER, and ZT491ER receivers have an
enable 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 that the receiver output will be in a HIGH-
IMPEDANCE state 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.
The ZT485ER, ZT490ER, and ZT491ER can transmit and
receiveatdataratesupto10Mbps. TheZT487E, ZT488ER,
and ZT489ER are specified for data rates up to 250kbps.
Specifications subject to change without notice
Zywyn
7
Febuary 2005
rev.1.2
5秒后页面跳转
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