LUCL8574DP-D AGERE [Agere Systems], LUCL8574DP-D Datasheet - Page 28

• Manufacturer Part Number: LUCL8574DP-D
• Description: L8574D Resistive Subscriber Line Interface Circuit(SLIC), Ring Relay,and Protector(SRP)for Long Loop and TR-57 Applications
• Manufacturer: AGERE [Agere Systems]

L8574D Resistive Subscriber Line Interface Circuit (SLIC), Ring
Relay, and Protector (SRP) for Long Loop and TR-57 Applications
dc Characteristics
V-I Characteristics
In longer loops, the L8574 will operate in the linear
region of operation, and in short loops, to conserve
power, the L8574 will operate in the (fixed) current-limit
region of operation. A typical V-I characteristic for the
L8574 is shown in Figure 10 below.
Note: V
Loop Length
The loop range is calculated as follows:
R
Where:
R
V
rent-limit circuit, typically 2.2 V.
I
at the maximum loop length, typically 18 mA.
|
assume 43.2 V.
R
R
1877 .
28
28
LIMIT
V
OHLIM
L
L
1
L
BAT
= ({
is the dc resistance of the subscriber loop.
= R
= ({43.2 V – 2.2 V}/0.018 A) – 200
|
is the minimum specified current that is required
Figure 10. Loop Current vs. Loop Voltage
BAT1
is the minimum magnitude of the battery—
|
2
is the overhead or drop associated with the cur-
V
50
40
30
20
10
= dc feed resistors = 200 .
0
BAT
= –48 V, V
0
|
– V
OHLIM
I
LIM
BAT2
10
10 k
= –48 V; I
}/I
1
LIMIT
LOOP VOLTAGE (V)
(continued)
20
(continued)
) – R
LIM
= 28 mA; R
1
400
–1
– R
30
=
2
R
–1
– 200
DC1
DC
40
= 400 .
12-3050.e (C)
=
50
ac Design
Codec Features and Selection Summary
There are four key ac design parameters:
At this point in the design, the codec needs to be select-
ed. The discrete network between the SLIC and the co-
dec can then be designed. Below is a brief codec
feature and selection summary.
First-Generation Codecs
These perform the basic filtering, A/D (transmit), D/A
(receive), and -law/A-law companding. They all have
an op amp in front of the A/D converter for transmit
gain setting and hybrid balance (cancellation at the
summing node). Depending on the type, some have
differential analog input stages, differential analog out-
put stages, and -law/A-law selectability. This genera-
tion of codec has the lowest cost. It is most suitable for
applications with fixed gains, termination impedance,
and hybrid balance.
Second-Generation Codecs
This class of devices includes a microprocessor inter-
face for software control of the gains and hybrid bal-
ance. The hybrid balance is included in the device. ac
programmability adds application flexibility and saves
several passive components. It also adds several I/O
latches that are needed in the application. It does not
have the transmit op amp, since the transmit gain and
hybrid balance are set internally.
Termination impedance is the impedance looking
into the 2-wire port of the line card. It is set to match
the impedance of the telephone loop in order to mini-
mize echo return to the telephone set.
Transmit gain is measured from the 2-wire port to
the PCM highway.
Receive gain is done from the PCM highway to the
transmit port.
Hybrid balance network cancels the unwanted
amount of the receive signal that appears at the
transmit port.
Lucent Technologies Inc.
October 1998
Data Sheet