STLC3055 datasheet(5/22 Pages) STMICROELECTRONICS

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The DC/DC converter controller is driving an ex-

ternal power MOS transistor (P-Channel) in order

to generate the negative battery voltage needed

for device operation.

The DC/DC converter controller is synchronised

with an external CLK (125KHZ typ.).

From version marked STLC3055 A5, it can be

synchronised to an internal clock generated when

the pin CLK is connected to CVCC. One sensing

resistor in series to Vpos supply allows to fix the

maximum allowed input peak current. This feature

is implemented in order to avoid overload on

Vpos supply in case of line transient (ex. ring trip

detection).

The typical value is obtained for a sensing resis-

tor equal to 110m

Ω that will guarantee an aver-

age current consumption from Vpos < 700mA.

When in on-hook the self generated battery volt-

age is set to a predefined value.

This value can be adjusted via one external resis-

tor (RF1) and it is typical -50V. When RING mode

is selected this value is increased to -70V typ.

Once the line goes in off-hook condition, the

DC/DC converter automatically adjust the gener-

ated battery voltage in order to feed the line with

a fixed DC current (programmable via RLIM) opti-

mising in this way the power dissipation.

OPERATING MODES

Power Down

DC CHARACTERISTIC & SUPERVISION

When this mode is selected the SLIC is switched

off and the TIP and RING pins are in high imped-

ance. Also the line detectors are disabled there-

fore the off-hook condition cannot be detected.

This mode can be selected in emergency condi-

tion when it is necessary to cut any current deliv-

ered to the line.

This mode is also forced by STLC3055 in case of

thermal overload (Tj > 140

°C).

In this case the device goes back to the previous

status as soon as the junction temperature de-

crease under the hysteresis threshold.

AC CHARACTERISTICS

The 2W port is set in high impedance, the TX

output buffer is a low impedance output, no AC

transmission is possible.

High Impedance Feeding (HI-Z)

DC CHARACTERISTIC & SUPERVISION

This operating mode is normally selected when

the telephone is in on-hook in order to monitor the

line status keeping the power consumption at the

minimum.

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(1500W+Rp)

in series (see fig.1), where Rp is the external pro-

tection resistance.

AC CHARACTERISTICS

The AC impedance shown at the 2W port

(TIP/RING) is the same as the DC

one. The

TIP/RING AC impedance will be 2x(1500

Ω + Rp)

or high impedance.

Active

DC CHARACTERISTICS & SUPERVISION

When this mode is selected the STLC3055 pro-

vides both DC feeding and AC transmission.

The STLC3055 feeds the line with a constant cur-

rent 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 STLC3055 behaves like a

40V voltage source with a series impedance

equal to the protection resistors 2xRp (typ.

2x41

Ω) plus the internal resistance. Fig. 2 shows

the typical DC characteristic in ACTIVE mode.

Vbat

Vbat (-50V)

2x(R1+Rp)

Slope: 2x(R1+Rp)

(R1=1500ohm)

Figure 1. DC Characteristic in HI-Z Mode.

STLC3055

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