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STLC3055

WLL & ISDN-TA SUBSCRIBER LINE INTERFACE CIRCUIT

STMicroelectronics 

STLC3055

Figure 2. DC characteristic in ACTIVE mode

IL

Ilim

(20 to

40mA)

2Rp

VL

10V

Vbat (-50V)

POLARITY REVERSAL

The D2 bit controls the line polarity, the transition

between the two polarities is performed in a "soft"

way. This means that the TIP and RING wire ex-

change their polarities following a ramp transition

(see fig.3). The transition time is controlled by an

external capacitor CREV. This capacitor is also

setting the shape of the ringing trapezoidal wave-

form.

When the control pins set battery reversal the line

polarity is reversed with a proper transition time

set via an external capacitor (CREV).

Figure 3. TIP/RING typical transition from

Direct to Reverse Polarity

The line status (on/off hook) is monitored by the

SLIC’s supervision circuit. The off-hook threshold

can be programmed via the external resistor RTH

in the range from 5mA to 9mA.

Independently on the programmed constant cur-

rent value, the TIP and RING buffers have a cur-

rent source capability limited to 70mA typ.

Moreover the power available at Vbat is control-

led by the DC/DC converter that limits the peak

current drawn from the Vpos supply. The maxi-

mum allowed current peak is set by the RSENSE

resistor and it is typically 900mApk.

AC CHARACTERISTICS

The SLIC provides the standard SLIC transmis-

sion functions:

Input impedance synthesis: can be real or

complex and is set by a scaled (x50) external

ZAC impedance.

Transmit and receive: The AC signal present

on the 2W port (TIP/RING) is transferred to the

TX output with a -6dB gain and from the RX in-

put to the 2W port with a 0dB gain.

2 to 4 wire conversion: The balance imped-

ance can be real or complex, the proper can-

cellation is obtained by means of two external

impedance ZA and ZB.

Once in Active mode (D1=1) the SLIC can oper-

ate in different states setting properly D0 and D2

control bits (see also Table 2).

Table 2. SLIC states in ACTIVE mode

D0 D1 D2

Operating Mode

0 1 0 Active Normal Polarity

0 1 1 Active Reverse Polarity

1 1 0 Active TTX injection (N.P.)

1 1 1 Active TTX injection (R.P.)

GND

TIP

4V typ.

dV/dT set

by CREV

RING

40V typ

ON-HOOK

METERING PULSE INJECTION (TTX)

The metering pulses circuit consist of a burst

shaping generator that gives a square wave

shaped and a low pass filter to reduce the har-

monic distortion of the output signal.

The metering pulse is obtained starting from two

logic signals:

CKTTX: is a square wave at the TTX fre-

quency (12 or 16KHz) and should be perma-

nently applied to the CKTTX pin or at least for

all the duration of the TTX pulse (including ris-

ing and decay phases).

D0: enable the TTX generation circuit and de-

fine the TTX pulse duration.

This two signals are then processed by a dedi-

cated circuitry integrated on chip that generate

the metering pulse as an amplitude modulated

shaped squarewave (SQTTX) (see fig.4).

Both the amplitude and the envelope of the

squarewave (SQTTX) can be programmed by

means of external components. In particular the

amplitude is set by the two resistors RLV and the

6/22

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