L8574D Datasheet, PDF (1/36 Pages) Agere Systems – L8574D Resistive Subscriber Line Interface Circuit(SLIC), Ring Relay,and Protector(SRP)for Long Loop and TR-57 Applications

Data Sheet
October 1998
L8574D Resistive Subscriber Line Interface Circuit (SLIC), Ring
Relay, and Protector (SRP) for Long Loop and TR-57 Applications
Features
s Low-power scan mode for low on-hook power dis-
sipation (55 mW max)
s Low active power dissipation; talk or on-hook
transmission (240 mW max)
s Distortion-free on-hook transmission
s Eight operating states via latched paralleled data
inputs with channel select feature
s Precision fixed 28 mA current limiter
s Integrated protection
s No external protection device required
s Integrated ringing access relay
s Ring trip detector
s Loop closure detector with hysteresis
s Relay driver
s Battery noise cancellation
s Thermal protection
s 44-pin, surface-mount, plastic package (PLCC)
Description
The L8574 is a resistive subscriber line interface cir-
cuit (SLIC) that is optimized for long loop applica-
tions, such as Bellcore TR-NWT-000057
requirements for digital loop carrier (DLC) applica-
tions. It interfaces the low-voltage circuits on an ana-
log line card to the Tip/Ring subscriber loop. The
L8574 does not supply dc current to the subscriber
loop; external resistors are used for this purpose.
Included in the L8574 are a solid-state ringing
access switch and a line break switch. Also included
is a relay driver for an external (test) access mechan-
ical relay.
State control is via four latched parallel data inputs. A
chip select feature allows the user to enable, disable,
or reset the data latches to a known logic state.
The L8574 offers a low-power scan state to minimize
power to less than 55 mW in the on-hook state. The
L8574 also supports on-hook transmission. The
active power in both the talk or on-hook transmission
mode is also very low (<240 mW). Current is limited
to a fixed value of 25 mA by an internal precision
current-limit circuit.
Because of the internal architecture of the L8574
SLIC and because of the power rating of the associ-
ated external feed resistors, the L8574 will meet most
surge requirements without use of an external sec-
ondary protection device. Internal circuitry steers
both positive and negative faults to fault ground. Neg-
ative faults are not dumped into battery.
The L8574 is a two-chip line interface solution pack-
aged in a single, 44-pin PLCC package. The Tip and
Ring drive amplifiers, the XMT amplifier, the receive
interface, and battery noise cancellation circuits are
fabricated in a 90 V complementary bipolar (CBIC)
process. The ring access switch, line break switch,
battery switch, current-limit, protection functions,
supervision, and control functions are fabricated in a
320 V dielectrically isolated bipolar-CMOS-DMOS
(BCDMOS) process. The device is available in a
44-pin PLCC package.