Functional description

STLC3085

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Transmit and receive: The AC signal present on the 2W port (TIP/RING) is transferred to

the TX output with a -6dB or -12dB gain and from the RX input to the 2W port with a 0dB or

+6dB gain.

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2 to 4 wire conversion: The balance impedance can be real or complex, the proper

cancellation is obtained by means of two external impedance ZA and ZB

Once in Active mode (D1=1) the SLIC can operate in different states setting properly D0 and

D2 control bits (see also Table 8).

Table 8.

SLIC states in ACTIVE mode

3.2.3.3 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 exchange their polarities following a ramp

transition (see Figure 5).

The transition time is controlled by an external capacitor CREV. This capacitor is also setting

the shape of the ringing trapezoidal waveform. When the control pins set battery reversal the

line polarity is reversed with a proper transition time set via an external capacitor (CREV).

Figure 5.

TIP/RING typical transition from Direct to Reverse Polarity

3.2.4

Ringing

When this mode is selected STLC3085 self generate an higher negative battery (-64V typ.) in

order to allow a balanced ringing signal of typically 59Vpeak.

In this condition both the DC and AC feedback loop are disabled and the SLIC line drivers

operate as voltage buffers. The ring waveform is obtained toggling the D2 control bit at the

desired ring frequency. This bit in fact controls the line polarity (0=direct; 1= reverse).

As in the ACTIVE mode the line voltage transition is performed with a ramp transition, obtaining

in this way a trapezoidal balanced ring waveform (see Figure 6).

The shaping is defined by the CREV external capacitor.

D0

D1

D2

Operating Mode

0

1

0

Active Normal Polarity

0

1

1

Active Reverse Polarity

GND

TIP

RING

dV/dT set

by CREV

4V typ.

38 V typ

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