STLC3055N_09 datasheet(11/34 Pages) STMICROELECTRONICS

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STLC3055N

Functional description

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The STLC3055N 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 typ.

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

constant current feed value, the STLC3055N behaves like a 40 V voltage source with a

series impedance equal to the protection resistors 2xRp (typ. 2 x 50

Ω). Figure 4 shows the

typical DC characteristic in Active mode.

Figure 4.

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 5 mA to 9 mA.

Independently on the programmed constant current value, the TIP and RING buffers have a

current source capability limited to 80 mA typ. 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.

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).

●

Input impedance synthesis: can be real or complex and is set by a scaled (x 50 or

x 25) external ZAC impedance.

●

Transmit and receive: The AC signal present on the 2W port (TIP and RING pins) is

transferred to the TX output with a -6 dB or -12 dB gain and from the RX input to the

2W port with a 0 dB or +6 dB gain.

●

2 to 4 wire conversion: The balance impedance can be real or complex, the proper

cancellation is obtained by means of two external impedance ZA and ZB

Once in Active mode (D1=1) the SLIC can operate in different states setting properly D0 and

D2 control bits (see also Table 8).

Table 7.

Gain set in active mode

Gain set

4 to 2 wire gain

2 to 4 wire gain

Impedance synthesis scale factor

0 dB

-6 dB

x 50

+6 dB

-12 dB

x 25

Ilim

Vbat (-50V)

10V

2Rp

(20 to

40mA)

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