ADM1490EBRMZ Analog Devices Inc, ADM1490EBRMZ Datasheet - Page 12

• Manufacturer Part Number: ADM1490EBRMZ
• Description: 5V Full Duplex RS-485 Tranceiver I.C.
• Manufacturer: Analog Devices Inc
• Type: Transceiverr

Specifications of ADM1490EBRMZ

• Number Of Drivers/receivers: 1/1
• Protocol: RS422, RS485
• Voltage - Supply: 4.75 V ~ 5.25 V
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADM1490E/ADM1491E
APPLICATIONS INFORMATION
DIFFERENTIAL DATA
Differential data transmission reliably transmits data at high
rates over long distances and through noisy environments.
Differential transmission nullifies the effects of ground shifts
and noise signals that appear as common-mode voltages on the
line. There are two main standards approved by the Electronics
Industries Association (EIA) that specify the electrical char-
acteristics of transceivers used in differential data transmission.
The RS-422 standard specifies data rates of up to 10 MBaud and
line lengths of up to 4000 feet. A single driver can drive a trans-
mission line with as many as 10 receivers.
The RS-485 standard addresses true multipoint communications.
This standard meets or exceeds all of the requirements of RS-422,
and it allows as many as 32 drivers and 32 receivers to connect
to a single bus. An extended common-mode range of −7 V to
+12 V is defined. The most significant difference between the
RS-422 and the RS-485 is that the drivers with RS-485 can be
disabled, allowing more than one driver to be connected to a
single line, with as many as 32 drivers connected to a single line.
Only one driver should be enabled at a time, but the RS-485
standard contains additional specifications to guarantee device
safety in the event of line contention.
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NOTES
1. MAXIMUM NUMBER OF NODES = 32.
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ADM1490E
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Figure 29. Typical Point-to-Point Full-Duplex Application
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CABLE AND DATA RATE
Twisted pair is the transmission line of choice for RS-485
communications. Twisted pair cable tends to cancel common-
mode noise and causes cancellation of the magnetic fields
generated by the current flowing through each wire, thereby
reducing the effective inductance of the pair.
An RS-485 transmission line can have as many as 32 trans-
ceivers on the bus. Only one driver can transmit at a time, but
multiple receivers may be enabled simultaneously.
As with any transmission line, it is important to minimize
reflections. This can be achieved by terminating the extreme
ends of the line using resistors equal to the characteristic
impedance of the line. Keep stub lengths of the main line as
short as possible. A properly terminated transmission line
appears purely resistive to the driver.
TYPICAL APPLICATIONS
Figure 29 shows a typical configuration for a full-duplex point-
to-point application using the ADM1490E. Figure 30 shows a
typical configuration for a full-duplex multipoint application
using the ADM1491E. To minimize reflections, the lines must
be terminated at the receiving end in its characteristic impedance,
and stub lengths off the main line must be kept as short as possible.
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ADM1490E
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