MAX14941 Datasheet, PDF (15/21 Pages) Maxim Integrated Products – 5kV Isolated 20Mbps Half-Duplex PROFIBUS

MAX14941/MAX14942
5kV Isolated 20Mbps Half-Duplex PROFIBUS/
RS-485 Transceivers with ±35kV ESD Protection
Detailed Description
The MAX14941/MAX14942 isolated PROFIBUS-DP/
RS-485 transceivers provide 2500VRMS (60s) of galvanic
isolation between the PROFIBUS-DP/RS-485 cableside
of the transceiver and the UART-side. These devices
allow fast (20Mbps) communication across an isolation
barrier when a large potential exists between grounds on
each side of the barrier.
Isolation
Data isolation is achieved using high-voltage capacitors
that allow data transmission between the UART-side and
the Profibus/RS-485 cable-side of the transceiver.
Integrated LDO
The devices include an internal low-dropout regulator with
a set 5V (typ) output that is used to power the cable-side
of the IC. The output of the LDO is VDDB. In addition to
powering the transceiver, VDDB can source up to 10mA,
allowing external termination resistors to be powered
without the need for an external regulator. The LDO has
a 300mA (typ) current limit. If the LDO is unused, connect
VLDO to GNDB and apply +5V directly to VDDB.
True Fail-Safe
The MAX14941/MAX14942 guarantee a logic-high on the
receiver output when the receiver inputs are shorted or
open, or when connected to a terminated transmission line
with all drivers disabled. The receiver threshold is fixed
between -50mV and -200mV. If the differential receiver
input voltage (VA – VB) is greater than or equal to -50mV,
RXD is logic-high. In the case of a terminated bus with all
transmitters disabled, the receiver’s differential input voltage
is pulled to zero by the termination resistors. Due to the
receiver thresholds of the MAX14941/MAX14942, this
results in a logic-high at RXD.
Driver Output Protection
Two mechanisms prevent excessive output current and
power dissipation caused by faults or bus contention. The
first, a foldback mode current limit on the output stage, provides
immediate protection against short circuits over the entire
common-mode voltage range. The second, a thermal-
shutdown circuit, forces the driver outputs into a
high-impedance state if the die temperature exceeds
+160°C (typ).
Thermal Shutdown
The devices are protected from overtemperature damage
by integrated thermal shutdown circuitry. When the junction
temperature (TJ) exceeds +160°C (typ), the driver outputs
go high-impedance. The device resumes normal operation
when TJ falls below +145°C (typ).
Applications Information
128 Transceivers on the Bus
The standard RS-485 receiver input impedance is one unit
load. A standard driver can drive up to 32 unit-loads. The
MAX14941/MAX14942 transceivers have a ¼-unit load
receiver, which allows up to 128 transceivers, connected
in parallel, on one communication line. Connect any com-
bination of these devices, and/or other RS-485 devices,
for a maximum of 32 unit-loads to the line.
Typical Application
The MAX14941/MAX14942 transceivers are designed
for bidirectional data communications on multipoint bus
transmission lines. Figure 10 and Figure 11 show typical
network application circuits. To minimize reflections, the
bus should be terminated at both ends in its characteristics
impedance, and stub lengths off the main line should be
kept as short as possible.
www.maximintegrated.com
Maxim Integrated │  15