STLC3055N_09 datasheet(10/34 Pages) STMICROELECTRONICS

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Functional description

STLC3055N

10/34

Once the line goes in off-hook condition, the DC/DC converter automatically adjust the

generated battery voltage in order to feed the line with a fixed DC current (programmable via

RLIM) optimising in this way the power dissipation.

4.2

Operating modes

4.2.1

Power down

When this mode is selected the SLIC is switched off and the TIP and RING pins are in high

impedance. Also the line detectors are disabled therefore the off-hook condition cannot be

detected.

This mode can be selected in emergency condition when it is necessary to cut any current

delivered to the line.

This mode is also forced by STLC3055N in case of thermal overload (Tj > 140 °C).

In this case the device goes back to the previous status as soon as the junction temperature

decrease under the hysteresis threshold.

No AC transmission is possible in this mode.

4.2.2

High impedance feeding (HI-Z)

This operating mode is normally selected when the telephone is in on-hook in order to

monitor the line status keeping the power consumption at the minimum.

The output voltage in on-hook condition is equal to the self generated battery voltage (-50 V

typ).

When off-hook occurs the DET becomes active (low logic level).

The off-hook threshold in HI-Z mode is the same value as programmed in ACTIVE mode.

The DC characteristic in HI-Z mode is just equal to the self generated battery with

2x(1600

Ω+Rp) in series (see Figure 3), where Rp is the external protection resistance.

No AC transmission is possible in this mode.

Figure 3.

DC characteristic in HI-Z mode.

4.2.3

Active

DC characteristics and supervision

When this mode is selected the STLC3055N provides both DC feeding and AC

transmission.

Vbat

Vbat (-50V)

2x(R1+Rp)

Slope: 2x(R1+Rp)

(R1=1600ohm)

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