Data Sheet
May 2001
L8576B Dual Ringing SLIC
Functional Description (continued)
Operating States
The L8576B device has four operating states:
Transmit and Receive Interface (continued)
■ Talk state—normal battery:
— Normal talk state.
— Battery feed is connected to the battery supply
(VBAT).
— Both receive and transmit transmission paths are
powered up.
— dc loop and instantaneous current limiters are
powered up and active.
A second gain setting is provided to accommodate ring
trip. A switch is built into TG2. In ringing mode, TG1
and TG2 are internally connected, thus shorting out the
external gain resistor RGX1. This provides a lower trans-
mit gain for ringing since ring trip is accomplished by
monitoring the voltage at DCOUT. This lower gain sets
DCOUT at the appropriate level to accommodate the
higher currents of the ring trip.
— NSTAT reflects the status of the switchhook
detector.
— PR is negative with respect to PT.
The receive interface circuitry couples the differential
signal on receive inputs RCVP and RCVN to the
tip/ring drivers.
■ Talk state—reverse battery:
— Normal talk state.
— Battery feed is connected to the battery supply
(VBAT).
Data Interface
— Both receive and transmit transmission paths are
powered up.
— dc loop current limiter is powered up and active.
— NSTAT reflects the status of the switchhook
detector.
A 4-wire parallel interface (B2, RNGNG, NDISC, and
NSTAT) is provided for each channel to control signals
to and from the system controller. B2 controls the for-
ward/reverse battery in normal talk mode while
RNGNG enables the balanced ringing mode of opera-
tion, and NDISC performs a disconnect state. NSTAT
reflects either the loop detector output or the ring trip
detector output, depending on the mode of the section.
It is the responsibility of the system controller to recog-
nize ring trip detection and set RNGNG to a logic 0
state to terminate ringing. The system controller should
also use RNGNG to set ringing cadence.
— PR is positive with respect to PT.
■ Ringing state:
— Normal ringing state.
— Both receive and transmit transmission paths are
inactive.
— Balanced ringing is applied to PR and PT, in
accordance with B2.
— Current limiter is set for ringing limit.
— NSTAT reflects the status of the ring trip detector.
— Only one channel should be in this state at a time
to control power dissipation.
Loop Current Detector
Each section of the device has an integral loop current
detector set at a nominal 12 mA of dc current. This is
used to detect off-hook transitions in the normal talk
state. When current less than the current threshold
(including no current) is flowing, NSTAT is at logic 1.
When loop current exceeds 12 mA, the output NSTAT
switches to a logic 0. No hysteresis is included.
■ Disconnect state:
— Tip and ring drive amplifiers are powered down.
— Pins PT and PR are high impedance (>100 kΩ).
— NSTAT is undefined.
— PT and PR voltage is undefined.
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Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
