XRT83VSH28IB datasheet(41/74 Pages) EXAR

41 / 74 page

PRELIMINARY

XRT83VSH28

REV. P1.0.0

8-CHANNEL E1 SHORT-HAUL LINE INTERFACE UNIT

4.3

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 XRT83VSH28 was

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.

4.4

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

4.5

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 XRT83VSH28’s internal

termination ensures that the line termination meets E1 specifications for 75

Ω 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 28.

FIGURE 28. SIMPLIFIED BLOCK DIAGRAM OF A NON-INTRUSIVE MONITORING APPLICATION

Line Card Transceiver

Non-Intrusive Receiver

Node

XRT83VSH28

Data Traffic

XRT83VSH28IB Datasheet(PDF) 41 Page - Exar Corporation