STLC3085

Functional description

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3.2.3

Active

3.2.3.1 DC characteristics & supervision

When this mode is selected the STLC3085 provides both DC feeding and AC transmission.

The STLC3085 feeds the line with a constant current fixed by RLIM (20mA to 25mA range).

The on-hook voltage is typically 38V allowing on-hook transmission; the self generated Vbat is -

46V typ.

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

current feed value, the STLC3085 behaves like a 38V voltage source with a series impedance

equal to the protection resistors 2xRp (typ. 2x50

Ω). Figure 4 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 65mA typ.

Figure 4.

DC characteristic in ACTIVE mode

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

resistor.

3.2.3.2 AC characteristics

The SLIC provides the standard SLIC transmission functions:

Once in active mode the SLIC can operate with two different Tx, Rx Gain. Setting properly by

the Gain set control bit (see Table 7).

Table 7.

Gain Set in Active Mode

●

Input impedance synthesis: can be real or complex and is set by a scaled (x50 or x25)

external ZAC impedance.

Gain set

4 to 2 wire Gain

2 to 4 wire Gain

Impedance Synthesis Scale Factor

0

0dB

-6dB

x 50

1

+6dB

-12dB

x 25

IL

Ilim

VL

Vbat (-46V)

10V

2Rp

(20 to

25mA)