STLC3080 datasheet(7/23 Pages) STMICROELECTRONICS

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- High Impedance Feeding :

entered after a Power-On Reset or 1XX word, this

status is set during steady On/Hook condition;

most of the circuitry is idle and only a low power

Off-Hook detection circuit is kept alive.

Direct Polarity only is assumed , independently of

the selected one.

To minimise the power consumption the Off-Hook de-

tectioncircuit has low common mode current rejection.

-Standby

Notice that in Stand-By state the Off-Hook detec-

tor is sensitive only to the transversal component

of the line current with high immunity to common

mode disturbances; this performance implies an

increasing in power consumption: for that reason

Stand-By is not used as a quiescent state.

- Active state gets operative for conversation af-

ter

an Off-Hook validity check performed in

Stand-By state, set after any Off-Hook detected in

High Impedance Feeding.

If the Off-Hook condition is confirmed in Stand By,

Active mode is set ; if not (in case of spurious de-

tection), false activation is prevented, and High

Impedance Feeding is resumed.

In order to have the device falling back in HI-feed-

ing mode after the line is back in on-hook condi-

tion. It is necessary to select as input state the ac-

tive direct polarity mode (default).

During Active state On/Off-Hook status will af-

fect in real time DET signalling bit.

In order to allow Pulse-Mode Dialling, once Ac-

tive state is set, it cannot be changed by fast On-

Hook , but it is turned back to High Impedance

Feeding

only if an On-Hook condition

lasts

longer than 128 x CKRING period.

Automatic activation (and deactivation) is based

on an internal state-machine which is clocked by

a free running internal oscillator.

A detailed description is reported in the Appendix A.

DUAL BATTERY CONFIGURATION

STLC3080 is also meant for low power consump-

tion systems using Dual Battery solution. It is suf-

ficient to connect the collector of the external tran-

sistor, through a diode, to the reduced battery

(see Fig. 2 for single battery solution and Fig. 3

for dual battery solution). The activation of the

batteries is automatic, only depending on the DC

load at the RING and TIP terminals; no controllers

action is required.

PROTECTION CIRCUIT

- Suggested protection circuit is based on pro-

grammable Trisils (like LCP1511/2) as shown

in Fig.2 and Fig. 3, and the surge current is

limited by the resistors RPT2 and RPR2, which

are PTC types , protecting the device against

both lightning and power-cross.

- Additionally, STLC3080 is provided with the

PCD input to directly monitor overvoltages ap-

plied to the line wires.

When the current injected into PCD exceeds a

threshold of 320

µA (+/- 30%) , DET and GDK/AL

are set Low signalling a fault condition. No

change on the SLIC mode is performed.

Voltage threshold is defined by proper value of

the series resistors (see Fig.1)

This circuit gives the possibility to protect the de-

vice against power crosses through a relay in-

stead of PTCs; once the fault condition is de-

tected

the

controller

drives

this

relay

disconnecting the Slic from the line terminals.

METERING PULSE INJECTION

STLC3080 provides external pins and compo-

nents for Metering Pulse injection. TTXIN pin is

the input for the 12kHz or 16kHz Metering Pulse

injection. This pin also provides a DC constant

current source that is injected into the external

RDA resistor (typ. 10k

Ω to obtain 2.2Vrms on

200

Ω) connected between TTXIN pin and AGND.

The voltage drop across TIP and RING line ampli-

fiers and, consequentallythe AC swing available.

When Metering Pulse injection is not used and

voltage drop is not required, TTXIN must be

shorted to AGND and RTTX, RDA and CTTX ex-

ternal components must be removed. The TTX

cancellation is obtained through an external

RTTX and CTTX network connected between

TTXIN and CAC pins.

Fault detection

The device provides current sense on TIP and

RING wires that allow to detect longitudinal DC

current (ILL). When this ILL current becomes

higher than a threshold (see detectors table in-

side electrical characteristics) a fault indication is

provided on DET and GDK pin (both outputs be-

come low). The fault indication is active till the

fault cause persists. With this circuit the following

fault condition can be detected.

TIP

to VB1

TIP

to GND

RING to VB1

RING to GND

RING to TIP to VB1

VCC

TIP

RING

PCD

DET

GDK/AL

D98TL385

CSOUT

Ith

Figure 1.

STLC3080

7/23

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