參數(shù)資料
型號(hào)： LXT331QE
英文描述： LINE INTERFACE|CMOS|QFP|44PIN|PLASTIC
中文描述： 線路接口|的CMOS | QFP封裝| 44PIN |塑料
文件頁(yè)數(shù)： 11/32頁(yè)
文件大?。?/td> 395K
代理商： LXT331QE
Dual T1/E1 Line Interface Unit
—
LXT331
Datasheet
11
a separate power supply pin (TVCC0 or TVCC1). Current limiters on the output drivers provide
short circuit protection. Refer to Test Specifications for TCLK timing characteristics. As shown in
Figure 3
, the LXT331 encodes transmit data using 50% Alternate Mark Inversion (AMI) line code.
2.2.1
Pulse Shape
The transmitted pulse shape is determined by Line Length equalizer control signals LEN0 through
LEN2. Equalizer codes are hard-wired in Hardware mode as shown in
Table 2
. In Host mode, the
LEN
control codes are input through the serial interface. Shaped pulses are applied to the AMI line
driver for transmission onto the line at TTIP and TRING. The line driver provides a constant Low
output impedance of < 3
(typical) regardless of whether it is driving marks or spaces or during
transitions. This well-controlled impedance provides excellent return loss when used with external
precision resistors (±1% accuracy). See
Table 9
and
Table 10
for recommended transformer
specifications, turns ratios, series resistor (Rt) values, and typical return losses for various LEN
codes. To minimize power consumption the DC blocking capacitor and the LXT331 can be
connected directly to a 1:1.15 transformer without series resistors.
Pulses can be shaped for either 1.544 or 2.048 Mbps applications. 1.544 Mbps pulses for DSX-1
applications can be programmed to match line lengths from 0 to 655 feet of 22 AWG ABAM cable.
A combination of 9.1
resistors and a 1:2.3 transformer is recommended for maximum transmit
return loss in DSX-1 applications. The LXT331 also matches FCC pulse mask specifications for
CSU applications.
The LXT331 produces 2.048 Mbps pulses for both 75
coaxial (2.37 V) or 120
shielded
twisted-pair (3.0 V) lines through an output transformer with a 1:2 turns ratio.
Refer to the
“
Application Information
”
on page 20
for details on interface circuitry.
2.2.2
Driver Performance Monitor
The LXT331 incorporates a Driver Performance Monitor (DPM) as shown in
Figure 4 on page 13
.
The DPM output goes High on receipt of 63 consecutive zeros (at MTIP and MRING) and returns
Low on receipt of a transition. A reset command also drives the output signal Low.
The LXT331 uses its MTIP and MRING pins to monitor its own TTIP and TRING outputs or those
of an adjacent chip. Mark detection involves two criteria:
1. Voltage threshold: a pulse must trip a threshold voltage above or below (depending on its
polarity) the input bias voltage level. The LXT331 bias voltage is 2.5 V and the threshold for a
mark is 2.5 ± 0.79 V.
Figure 3. 50% AMI Coding
BIT CELL
TTIP
TRING
1
0
1
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