LXT331
—
Dual T1/E1 Line Interface Unit
20
Datasheet
3.0
Application Information
3.1
Power Requirements
The LXT331 is a low-power CMOS device. Three separate power pins are provided: one pin for
each port
’
s transmitter circuits (TVCC0 and TVCC1) and a pin for all remaining circuits (VCC).
The LXT331 typically operates from a single +5 V power supply that is tied to all three VCC
inputs. Note that all power pins must be within ±0.3 V of each other, and decoupled to their
respective grounds separately. Isolation between the transmit and receive circuits is provided
internally. During normal operation or analog loopback, the transmitter powers down when TCLK
is not supplied.
3.1.1
Line Interface Requirements
Table 6
lists transformer values for 1.544 Mbps and 2.048 Mbps applications.
Table 7
shows
combinations of transformers, series resistors and the LEN control settings that produce a variety
of return loss values.
Table 6. Recommended Transmit Transformer Values
Parameter
Value
Turns Ratio (T1)
1:2/1:1.15/1:2.3 (Tx)/
1:1 (Rx)
Turns Ratio (E1)
1:2 (Tx) / 1: 1 (Rx)
Primary Inductance
1.2 mH minimum
Leakage Inductance
0.5
μΗ
maximum
Interwinding Capacitance
25 pF maximum
DC Resistance (Primary)
1
maximum
ET (Breakdown Voltage)
1 kV minimum
Table 7. Transmit Transformer Combinations
LEN
Xfmr Ratio
1
Rt Value
2
Rtn Loss
3
For T1/DSX-1 100
Twisted-Pair Applications:
011-111
1:2
Rt = 9.1
14dB
011-111
1:2.3
Rt = 9.1
18dB
011-011
1:1.15
Rt = 0
1dB
For E1 120
Twisted-Pair Applications:
001
1:2
Rt = 15
18dB
000
1:2
Rt = 9.1
10dB
1. Transformer turns ratio accuracy is ± 2%.
2. Rt values are ± 1%.
3. Typical return loss, 51kHz - 3.072 MHz band, with a
capacitor in parallel with the primary side of the transformer.