ADM4850 Просмотр технического описания (PDF) - Analog Devices
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ADM4850 Datasheet PDF : 16 Pages
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ADM4850/ADM4851/ADM4852/ADM4853/ADM4854/ADM4855/ADM4856/ADM4857
CIRCUIT DESCRIPTION
The ADM4850/ADM4851/ADM4852/ADM4853/ADM4854/
ADM4855/ADM4856/ADM4857 are high speed RS-485/
RS-422 transceivers offering enhanced performance over
industry-standard devices. All devices in the family contain
one driver and one receiver, but offer a choice of performance
options. The devices feature true fail-safe operation, which
means that a logic high receiver output is guaranteed when
the receiver inputs are open-circuit or short-circuit, or when
they are connected to a terminated transmission line with all
drivers disabled (see the Fail-Safe Operation section).
SLEW-RATE CONTROL
The ADM4850 and ADM4854 feature a controlled slew-rate
driver that minimizes electromagnetic interference (EMI) and
reduces reflections caused by incorrectly terminated cables,
allowing error-free data transmission rates up to 115 kbps. The
ADM4851 and ADM4855 offer a higher limit on driver output
slew rate, allowing data transmission rates up to 500 kbps. The
driver slew rates of the ADM4852 and ADM4856 and the
ADM4853 and ADM4857 are not limited, offering data
transmission rates up to 2.5 Mbps and 10 Mbps, respectively.
RECEIVER INPUT FILTERING
The receivers of all the devices incorporate input hysteresis. In
addition, the receivers of the 115 kbps ADM4850 and ADM4854
and the 500 kbps ADM4851 and ADM4855 incorporate input
filtering. This enhances noise immunity with differential signals
that have very slow rise and fall times. However, it causes the
propagation delay to increase by 20%.
HALF-/FULL-DUPLEX OPERATION
Half-duplex operation implies that the transceiver can transmit
and receive, but it can do only one of these at any given time. How-
ever, with full-duplex operation, the transceiver can transmit and
receive simultaneously. The ADM4850/ADM4851/ADM4852/
ADM4853 are half-duplex devices in which the driver and the
receiver share differential bus terminals. The ADM4854/
ADM4855/ADM4856/ADM4857 are full-duplex devices that
have dedicated driver output and receiver input pins. Figure 28
and Figure 29 show typical half- and full-duplex topologies.
ADM4850/ADM4851/
ADM4852/ADM4853
RO
R
A
RE
DE
DI
D
B
A
B
A
B
ADM4850/ADM4851/
ADM4852/ADM4853
A
R
RO
RE
DE
B
D
DI
R
D
R
D
RO RE DE DI
RO RE DE DI
MAXIMUM NUMBER OF TRANSCEIVERS ON BUS: 256
Figure 28. Typical Half-Duplex RS-485 Network Topology
VCC
VCC
ADM4854/ADM4855/
ADM4856/ADM4857 A
RO
R
B
Z
DI
D
Y
ADM4854/ADM4855/
ADM4856/ADM4857
Y
D
DI
Z
B
R
RO
A
GND
GND
Figure 29. Typical Full-Duplex Point-to-Point RS-485 Network Topology
Rev. D | Page 13 of 16
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