STLC3065 datasheet(8/27 Pages) STMICROELECTRONICS

8 / 27 page

in series (see fig.2), where Rp is the external pro-

tection resistance.

It should be noted that in case of both ports in HI-

Z mode and both of them in off-hook condition the

power dissipated inside the chip could drive the

device in thermal protection. This can be pre-

vented via a proper software control that should

avoid to keep as a steady condition both lines in

off-hook and HI-Z mode. Typical operation is to

set the SLIC core in active mode as soon as off-

hook is detected.

AC CHARACTERISTICS

The AC impedance shown at the 2W ports

(TIP1/RING1 and TIP2/RING2) is the same as

the DC one. Depending on the P1, P2 bits the

TIP1/RING1 and TIP2/RING2 AC impedance will

be 2x(1500

Ω + Rp) or high impedance.

Active

DET

DET1

DET2

disable

off/hk

line 1+2

disable

off/hk

line 2

disable

off/hk

line 1

disable

DC CHARACTERISTICS & SUPERVISION

When this mode is selected it is because one

connected telephone goes off-hook and the

STLC3065 is providing both DC feeding and AC

transmission.

The SLIC core is in ACTIVE mode and normally

only one of the two port should be connected to it:

P1,P2 = (1,0) or (0,1). (see Fig.1 and Table 2).

The unselected port is anyway DC biased being

TIP wire connected to BGND via a 1600W resis-

tor and the RING wire connected to a 300mA

(min.) current source connected to Vbat.

It should be noted that since Vbat is self gener-

ated by the STLC3065 and it is tracking the line

voltage depending on the loop resistance con-

nected to the selected port its voltage can range

typically from -12V to -50V. The unselected port

status (on/off hook) cannot be detected. For spe-

cial configurations it is also possible to set AC-

TIVE mode with both port selected (P1,P2=1,1) or

both unselected (P1,P2=0,0).

Considering now the selected port, this is con-

nected to the SLIC core. The STLC3065 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 -52V typ.

If the loop resistance is very high and

the line

current cannot reach the programmed constant

current feed value, the STLC3065 behaves like a

40V voltage source with a series impedance

equal to the protection resistors 2xRp(typ. 2x41

Ω)

plus the line series switches (Sw1 or Sw2) on re-

sistance 2xRsw (typ. 2x9

Ω).

Fig.3 shows the typical DC characteristic in AC-

TIVE mode.

The line status (on/off hook) is monitored by the

SLIC core Supervision circuit. The off-hook

threshold can be programmed via the external

resistor RTH in the range from 5mA to 9mA.

When the line goes in off-hook condition the built

in DC/DC converter controller set properly the

Vbat supply in order to keep the loop current fixed

to the programmed value.

Independently on the programmed constant cur-

rent value, the TIP and RING buffers have a cur-

rent source capability limited to 70mA typ.

Vbat

Vbat (-50V)

Slope: 2x(R1+Rp)

(R1=1500ohm)

2x(R1+Rp)

Figure 2. DC characteristic in HI-Z mode.

Ilim

Vbat (-50V)

10V

2Rp+2Rsw

(100ohm typ.)

(20 to

40mA)

Figure 3. DC characteristicin ACTIVE mode

STLC3065

8/27

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