LUCL8574DP-D AGERE [Agere Systems], LUCL8574DP-D Datasheet - Page 18

• 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
Operating States
Intermediate Talk State
Applications
General
The L8574 supplies a precise differential current to the
Tip/Ring pair (via PT and PR) as a function of analog
signals on IRCV and RCVN. However, the current driv-
ers connected to PT and PR are not designed to supply
dc feed current to the loop. The dc loop current is fed by
two external 200
hook), the battery switch (SW1) is turned on to connect
the Ring lead to V
viding sufficient Tip/Ring open circuit voltage to operate
various types of customer premises equipment (CPE).
Transmission may or may not be enabled in the idle dc
feed condition. If transmission is enabled (on-hook
transmission), the current drivers are biased so that
they can both source and sink sufficient signal current
when no dc loop current is flowing (even in the pres-
ence of longitudinal currents on Tip and Ring). When
the loop is off-hook, the battery switch (SW1) is turned
off and the current limiter becomes active. This con-
nects the Ring lead to V
an accurate current limiter circuit which saves off-hook
power dissipation. To ensure proper ac performance,
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Talk state with an increased and current-limited out-
put impedance.
Same as talk state.
The current limiter is powered up and active, but the
output capacitance at V
mately 350 times I
V
sion to the talk state.
A 10 mA dc bias current flows out of the Ring current
driver into PR, and a 5 mA dc bias current flows into
the Tip current driver from PT (the switchhook detec-
tor and current limiter are adjusted to compensate for
this dc bias current).
SW2 is closed; SW1 and SW3 are open.
NSTAT reflects the status of the switchhook detector.
BF
voltage during transitions from on-hook transmis-
BAT1
resistors. When a loop is idle (on-
LIM
which is typically –48 V, thus pro-
. This allows rapid settling of the
BAT2
(continued)
BF
(typically –48 V) through
is reduced to approxi-
the ac output impedance of the current limiter must be
small. The effective output capacitance at V
approximately 7500 times C
is active.
The external 200
part, determine the longitudinal balance of the SLIC;
thus, they must be matched appropriately to meet the
longitudinal balance requirements (0.2% for 58 dB bal-
ance, 0.35% for 52 dB balance). The impedance of the
battery switch and current limiter in series with the ring-
side dc feed resistor is reduced by the battery noise
cancellation circuit so that it has minimal effect on the
longitudinal balance. The dc feed resistors also have a
significant impact on the termination impedance of the
SLIC. Feedback, using external components, allows
the user to adjust the termination impedance from the
400
complex termination impedances. Because the L8574
does not supply dc feed current to the loop outputs, PT
and PR can be coupled to the Tip and Ring through a
sufficiently high resistance to allow for simple lightning
protection of the drivers. However, the resistance must
be low enough to achieve the coupling of sufficient ac
signal to the Tip and Ring from the available power
supply. Since the Tip and Ring drivers are current
sources, the value of this resistance does not affect the
performance of the SLIC and is somewhat arbitrary.
The value chosen is typically 1000 .
The L8574 also senses the differential Tip/Ring voltage
via sense inputs TS and RS. The differential dc voltage
is used internally for switchhook detection. The detec-
tor threshold is preset internally. The differential Tip/
Ring ac signal appears on analog output XMT. Also
included on the L8574 are SCR protectors, a relay
driver, one logic output (indicates switchhook and ring
trip status), a 4-bit parallel logic interface, a ringing
access switch, a ring trip detector, and a circuit which
eliminates the battery noise that is coupled to the Tip
and Ring through the dc feed resistors.
The following diagram and table show the basic com-
ponents required with the L8574 SLIC. Specific compo-
nent values are given in cases where the value is fixed.
In cases where the value may change (i.e., compo-
nents that determine the ac interface), the value is not
listed but equations to determine these values are
given later in this document.
dc feed resistance to satisfy most resistive and
dc feed resistors will, for the most
LIM
Lucent Technologies Inc.
when the current limiter
October 1998
Data Sheet
BF
is