L8576B 데이터 시트보기 (PDF) - Agere -> LSI Corporation

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L8576B

Dual Ringing SLIC

Agere -> LSI Corporation 

L8576B Dual Ringing SLIC

Data Sheet

May 2001

Functional Description (continued)

Operating States

Transmit and Receive Interface (continued)

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.

The receive interface circuitry couples the differential

signal on receive inputs RCVP and RCVN to the

tip/ring drivers.

Data Interface

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.

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.

The L8576B device has four operating states:

s 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.

— NSTAT reflects the status of the switchhook

detector.

— PR is negative with respect to PT.

s Talk state—reverse battery:

— Normal talk state.

— Battery feed is connected to the battery supply

(VBAT).

— 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.

— PR is positive with respect to PT.

s 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.

s 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.

8

Agere Systems Inc.

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