LXT386LE datasheet(27/78 Pages) INTEL

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QUAD T1/E1/J1 Transceiver — LXT386

Datasheet

3.3.2

Transmit Pulse Shaping

The transmitted pulse shape is internally generated using a high speed D/A converter. Shaped

pulses are further applied to the line driver for transmission onto the line at TTIP and TRING. The

line driver provides a constant low output impedance regardless of whether it is driving marks.

3.3.2.1

Output Driver Power Supply

The output driver power supply (TVCC pins) can be either 3.3V or 5V nominal. When TVCC=5V,

LXT386 drives both E1 (75

Ω/120Ω) and T1 100Ω lines through a 1:2 transformer and 11Ω/9.1Ω

series resistors.

When TVCC=3.3V, the LXT386 drives E1 (75

Ω/120Ω) lines through a 1:2 transformer and 11Ω

series resistor. A configuration with a 1:2 transformer and without series resistors should be used to

drive T1 100

Ω lines.

Removing the series resistors for T1 applications with TVCC=3.3V, improves the power

consumption of the device. See Table 35.

On the other hand, series resistors in the transmit configuration improve the transmit return loss

performance. Good transmit return loss performance minimizes reflections in harsh cable

environments. In addition, series resistors provide protection against surges coupled to the device.

The resistors should be used in systems requiring protection switching without external relays.

Please refer to Figure 7 for the recommended external line circuitry.

3.3.2.2

Power Sequencing

For the LXT384, we recommend sequencing TVCC first then VCC second or at the same time as

TVCC to prevent excessive current draw.

3.4

Driver Failure Monitor

The LXT386 transceiver incorporates an internal power Driver Failure Monitor (DFM) in parallel

with TTIP and TRING that is capable of detecting secondary shorts without cable. DFM is available

only in configurations with no transmit series resistors (T1 mode with TVCC=3.3V). This feature is

available in the serial and parallel host modes but not available in the hardware mode of operation.

Table 2.

Line Length Equalizer Inputs

LEN2

LEN1

LEN0

Line Length1

Cable Loss2

Operation Mode

0 - 133 ft. ABAM

133 - 266 ft. ABAM

266 - 399 ft. ABAM

399 - 533 ft. ABAM

533 - 655 ft. ABAM

0.6 dB

1.2 dB

1.8 dB

2.4 dB

3.0 dB

E1 G.703, 75

Ω coaxial cable and 120 Ω twisted pair cable.

1. Line length from LXT386 to DSX-1 cross-connect point.

2. Maximum cable loss at 772KHz.

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