il3122 NVE Corp., il3122 Datasheet - Page 9

• Manufacturer Part Number: il3122
• Description: Low Cost Rs-485 And Rs-422 Isolated Transceivers
• Manufacturer: NVE Corp.

Terminations:
Transmission lines should be terminated to avoid reflections that cause data errors. In RS-485 systems both ends of the bus, not
every node, should be terminated. In RS-422 systems only the receiver end should be terminated.
Proper termination is imperative when using IL3185 and IL3122 to minimize reflections. Unterminated lines are only suitable for
very low data rates and very short cable runs, otherwise line reflections cause problems. Parallel terminations are the most popular.
They allow high data rates and excellent signal quality.
Occasionally in noisy environments, fast pulses or noise appearing on the bus lines cause errors. One way of alleviating such errors
without adding circuit delays is to place a series resistor in the bus line. Depending on the power supply, the resistor should be
between 300 Ω (3 V supply) and 500 Ω (5 V supply).
Typical Coil Connections
V
V
V
NVE Corporation
DE
DD1
DD1
DD1
D
16pF ±50%
16pF ±50%
= V
= 3.3 V
V
Figure 3. Cable Length vs. Data Rate (30% jitter).
COIL1
R1
R2
RE
DD2
R
= 5 V
11409 Valley View Road, Eden Prairie, MN 55344-3617
Cable Length (feet)
R1, R2 = 590 Ω;  R 3 = 931 Ω
R1, R2, R3 = 931 Ω
V
COIL2
4000
1000
Unterminated
100
40
16pF ±50%
100
A
B
R3
V
1K
DD2
Data Rate (bps)
10K
Phone: [phone]
9
V
V
V
DE
DD1
100K
DD1
DD1
D
16pF ±50%
16pF ±50%
= V
= 3.3 V
V
R1
R2
COIL1
RE
R
DD2
1M
Fax: [phone]
= 5 V
100 Ω
Parallel
10M
R1, R2 = 590 Ω;  R 3 = 931 Ω
www.IsoLoop.com
IL3185/IL3122
R1, R2, R3 = 931 Ω
V
COIL2
Y
Z
A
B
R3
16pF ±50%
©2008 NVE Corporation
V
DD2