STLC3075_09 datasheet(11/36 Pages) STMICROELECTRONICS

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STLC3075

Functional description

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4.2.3

Active

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 (20 mA to 40 mA

range). The on-hook voltage is typically 40 V allowing on-hook transmission; the self

generated Vbat is -50 V typical.

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

constant current feed value, the STLC3075 behaves like a 40 V voltage source with a series

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

Ω). Figure 4. shows the typical

DC characteristics 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 typical.

Figure 4.

DC characteristics in active mode

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

peak current drawn from the VPOS supply. The maximum allowed current peak is set by

RSENSE resistor.

Ilim

Vbat (-50V)

10V

2Rp

(20 to

40mA)

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