Functional description

STLC3085

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Typ. value of 220m

Ω guarantees an average current consumption from Vpos < 800mA for Fly-

Back configuration

The self generated battery voltage is set to a predefined value in on-hook state.

This value can be adjusted via one external resistor (RF1) and it is typical -46V. When RING

mode is selected this value is increased to -64V typ.

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

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

RLIM) optimising the power dissipation.

3.2

Operating modes

3.2.1

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 STLC3085 in case of thermal overload

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

3.2.2

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 (-46V 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 possibile.

Figure 3.

DC Characteristic in HI-Z Mode.

Vbat

IL

VL

Vbat (-46V)

2x(R1+Rp)

Slope: 2x(R1+Rp)

(R1=1500ohm)