STLC3075

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The output voltage in on-hook condition is equal to the self generated battery voltage (-50V 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 fig. 4), where Rp is the external protection resistance.

No AC transmission is possibile.

Figure 4. DC Characteristic in HI-Z Mode.

3.2.3 Active

3.2.3.1 DC Characteristics & Supervision

When this mode is selected the STLC3075 provides both DC feeding and AC transmission.

The STLC3075 feeds the line with a constant current fixed by RLIM (20mA to 40mA range). The on-hook

voltage is typically 40V allowing on-hook transmission; the self generated Vbat is -50V typ.

If the loop resistance is very high and the line current cannot reach the programmed constant current feed

value, the STLC3075 behaves like a 40V voltage source with a series impedance equal to the protection

resistors 2xRp (typ. 2x50

Ω). Fig. 5 shows the typical DC characteristic in ACTIVE mode.

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 current value, the TIP and RING buffers have a current

source capability limited to 80mA typ.

Figure 5. DC characteristic in ACTIVE mode

Moreover the power available at Vbat is controlled by the DC/DC converter that limits the peak current

Vbat

IL

VL

Vbat (-50V)

2x(R1+Rp)

Slope: 2x(R1+Rp)

(R1=1600ohm)

IL

Ilim

VL

Vbat (-50V)

10V

2Rp

(20 to

40mA)