STLC3065 datasheet(9/27 Pages) STMICROELECTRONICS

9 / 27 page

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 core provides the standard SLIC trans-

mission 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 core can

operate in different states setting properly D0 and

D2 control bits (see also Table3).

Operating state

Active Normal Polarity

Active Reverse Polarity

Active TTX injection (N.P.)

Active TTX injection (R.P.)

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.4). 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).

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.5).

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

shaping by the capacitor CS.

The waveform so generated is then filtered and

injected on the line. The low pass filter can be ob-

tained using the integrated buffer OP1 connected

between pin FTTX (OP1 non inverting input) and

RTTX (OP1 output) (see fig.5) and implementing

a ”Sallen and Key” configuration.

Depending on the external components count it is

possible to build an optimised

application de-

pending on the distortion level required. In par-

ticular harmonic distortion levels equal to 13%,

6% and 3% can be obtained respectively with

first, second and third order filters (see fig.5).

The circuit shown in the ”Application diagram” is

related to the simple first order filter.

Once the shaped and filtered signal is obtained at

RTTX buffer output it is injected on the TIP/RING

pins with a +6dB gain.

It should be noted that this is the nominal condi-

tion obtained in presence of ideal TTX echo can-

cellation (obtained via proper setting of RTTX and

CTTX). In addition the effective level obtained on

the line will depend on the line impedance, the

protection resistor value and the series switch

(SW1 or SW2) on resistance.

In the typical application (TTX line impedance

=200

Ω , RP=41Ω, SW1,2 on resistance = 9Ω and

ideal TTX echo cancellation) the metering pulse

level on the line will be 1.33 times the level ap-

plied to the RTTX pin.

GND

TIP

RING

dV/dT set

by CREV

4V typ.

40V typ

ON-HOOK

Figure 4. TIP/RING typical transition from

Direct to Reverse Polarity

STLC3065

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