le5711 Zarlink Semiconductor, le5711 Datasheet - Page 3

• Manufacturer Part Number: le5711
• Description: Dual Subscriber Line Interface Circuit
• Manufacturer: Zarlink Semiconductor

Le5711
Data Sheet
PRODUCT DESCRIPTION
The Le5711 device is designed for long loop high-density POTS applications requiring a low power, small footprint SLIC. The
Le5711 device increases linecard density by integrating two SLIC devices into a single 32 pin package. This reduction in board
space allows for higher density linecard, which allows for amortizing common hardware across more channels. The Le5711
device gives linecard designers a simple control interface that supports four states: Active, Reverse Polarity, Standby, and
Disconnect (Ringing). The Le5711 device is low cost and high performance, providing key features required for POTS markets
requiring only loop start. The device includes a thermal management resistor for reducing power dissipation.
BLOCK DESCRIPTIONS
Two-Wire Interface
The two-wire interfaces provide DC current and send voice signals to a telephone apparatus connected to the linecard with a
two-wire line. The two-wire interface also receives the returning voice signals from the telephone transmitter.
Signal Transmission
The RSN input current controls the receive current sent to the two-wire interface. The AC line voltage is sensed by a differential
amplifier between the A
(TIP) and HP
leads.* The output of this amplifier is equal to the AC metallic components of the line
i
i
voltages and is output at VTX
. The transmission circuit also contains a longitudinal feedback circuit to shunt longitudinal signals
i
to a DC bias voltage. The longitudinal feedback does not affect metallic signals.
*Note:
"i" denotes channel number
Power Feed Controller and Common Bias
The power feed controllers have three sections: (1) the battery feed circuit, (2) the reverse polarity circuit, and (3) the common
bias circuit. The battery feed circuit regulates the amount of DC current and voltage supplied to the telephone over a wide range
of loop resistance. The reverse polarity circuit provides the capability to reverse the loop current for pay telephone key pad disable
and other applications. The bias circuit provides a filtered reference voltage, which is offset from the subscriber line voltage, and
a signal which sets the current limit.
Input Decoder and Control
The input decoder and control block provides a means for a microprocessor or SLAC IC to control such system states as Active,
Standby, Disconnect (Ringing), and Reverse Polarity. The input decoder and control block has TTL-compatible inputs, which set
the operating states of the SLIC device. It also provides the supervision signal sent back to the controller.
Off-Hook Detector
The most important loop monitoring function is off-hook detection. Loop current is programmed for both channels by a single
resistor. Loop detect threshold is typically 1/3 of the programmed Loop current in the Active and Reverse Polarity states.
Ring-Trip Detector
In the Disconnect state, the ring-trip detector is active. While the DB
pin is more negative than the DAC pin, the DET pin will be
i
high to indicate on hook. When an off hook condition occurs, the DB
pin becomes more positive than the DAC pin, and the DET
i
pin will go low to indicate off hook during ringing (ring-trip) has been detected. The system implements the Ringing state using
external control of a ring relay in combination with the Disconnect SLIC state, which enables the ring-trip detector.
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Zarlink Semiconductor Inc.