XRT83SL28
xr
8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT
REV.1.0.0
3.3
Power Failure Protection
For 1:1 or 1+1 line card redundancy in E1 applications, power failure could cause a line card to change the
characteristics of the line impedance, causing a degradation in system performance. The XRT83SL28 is
designed to ensure reliability during power failures. The LIU has patented high impedance circuits that allow
the receiver inputs and the transmitter outputs to be in "High" impedance when the LIU experiences a power
failure or when the LIU is powered off.
NOTE: For power failure protection, a transformer must be used to couple to the line interface. See the TAN-56 application
note for more details.
3.4
Overvoltage and Overcurrent Protection
Physical layer devices such as LIUs that interface to telecommunications lines are exposed to overvoltage
transients posed by environmental threats. An Overvoltage transient is a pulse of energy concentrated over a
small period of time, usually under a few milliseconds. These pulses are random and exceed the operating
conditions of CMOS transceiver ICs. Electronic equipment connecting to data lines are susceptible to many
forms of overvoltage transients such as lightning, AC power faults and electrostatic discharge (ESD). There
are three important standards when designing a telecommunications system to withstand overvoltage
transients.
• UL1950 and FCC Part 68
• Telcordia (Bellcore) GR-1089
• ITU-T K.20, K.21 and K.41
NOTE: For a reference design and performance, see the TAN-54 application note for more details.
3.5
Non-Intrusive Monitoring
In non-intrusive monitoring applications, the transmitters are shut off by setting TxON "Low". The receivers
must be actively receiving data without interfering with the line impedance. The XRT83SL28’s internal
termination ensures that the line termination meets E1 specifications for 75Ω or 120Ω while monitoring the data
stream. System integrity is maintained by placing the non-intrusive receiver in "High" impedance, equivalent to
that of a 1+1 redundancy application. A simplified block diagram of non-intrusive monitoring is shown in
Figure 25.
FIGURE 25. SIMPLIFIED BLOCK DIAGRAM OF A NON-INTRUSIVE MONITORING APPLICATION
XRT83SL28
Line Card Transceiver
Data Traffic
Node
XRT83SL28
Non-Intrusive Receiver
30
EXAR [ EXAR CORPORATION ]
