STLC3075_09 datasheet(15/36 Pages) STMICROELECTRONICS

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STLC3075

Functional description

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Once the ring trip is detected, the DET output is activated (logic level low). At this point the

card controller or a simple logic circuit stops the D2 toggling in order to effectively

disconnect the ring signal and then set the STLC3075 in the proper operating mode

(normally active).

Ring level in presence of more telephones in parallel

As already mentioned in the previous section, the maximum current that can be drawn from

the VPOS supply is controlled and limited via the external RSENSE. This also limits the power

available at the self generated negative battery.

If for any reason the ringer load is too low, the self generated battery drops in order to keep

the power consumption to the fixed limit and consequently the ring voltage level is also

reduced.

In the typical buckboost configuration with RSENSE = 110 mΩ the peak current from VPOS is

limited to around 900 mApk, which correspond to an average current of 700 mA max. In this

condition the STLC3075 can drive up to 3REN with a ring frequency fr=25 Hz

(1REN = 1800

Ω + 1.0 µF, European standard).

In order to drive up to 5REN (1REN= 6930

Ω + 8 µF, US standard) it is necessary to modify

the external components as follows:

CREV = 15nF; RD = 2.2 k

Ω; R

SENSE = 100 mΩ.

In flyback configuration the value of RSENSE = 220 mΩ guarantees to match both European

and USA standards. In order to drive 5REN (US standard) it is necessary to modify the

external component: RD = 2.2 kΩ.

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