5/25

STLC3055N

Table 6 shows how to set the different SLIC operating modes.

Table 6. SLIC Operating Modes.

3.1 DC/DC Converter

The DC/DC converter controller is driving an external power MOS transistor (P-Channel) in order to gen-

erate the negative battery voltage needed for device operation.

The DC/DC converter controller is synchronised with an external CLK (125KHz typ.)or with 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 over-

load on Vpos supply in case of line transient (ex. ring trip detection).

The typical value is obtained for a sensing resistor equal to 110m

Ω that will guarantee an average current

consumption from Vpos < 700mA. When in on-hook the self generated battery voltage is set to a pre-

defined value.

This value can be adjusted via one external resistor (RF1) and it is typical -50V. When RING mode is se-

lected this value is increased to -70V typ.

Once the line goes in off-hook condition, the DC/DC converter automatically adjust the generated battery

voltage in order to feed the line with a fixed DC current (programmable via RLIM) optimising in this way

the power dissipation.

3.2 OPERATING MODES

3.2.1 Power Down

When this mode is selected the SLIC is switched off and the TIP and RING pins are in high impedance.

Also the line detectors are disabled therefore the off-hook condition cannot be detected.

This mode can be selected in emergency condition when it is necessary to cut any current delivered to the

line.

In this case the device goes back to the previous status as soon as the junction temperature decrease

under the hysteresis threshold.

No AC transmission is possible in this mode.

3.2.2 High Impedance Feeding (HI-Z)

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).

PD

D0

D1

D2

Operating Mode

0

0

0

X

Power Down

1

0

0

X

H.I. Feeding (HI-Z)

1

0

1

0

Active Normal Polarity

1

0

1

1

Active Reverse Polarity

1

1

1

0

Active TTX injection (N.P.)

1

1

1

1

Active TTX injection (R.P.)

1

1

0

0/1

Ring (D2 bit toggles @ fring)