L3000S datasheet(9/29 Pages) STMICROELECTRONICS

9 / 29 page

stem ; in this case the internal dropout voltage is

equal to 30V.

Fig. 3 shows the DC characteristic in boost battery

condition.

In conversationmode, on request of control proces-

sor, whatever condition is set (normal or boost bat-

tery, direct or reverse polarity), you can inject the

12kHz (or 16kHz) signal (permanentlyapplied at the

pin 33 with 950mVrms typ. amplitude), as metering

pulses. A patented automatic control system adjust

the level of the metering signal, across the line, to

2Vrms setting BIT3 = 0, or to 5Vrms setting BIT3 =

1 ; this, regardless of the line impedance. Moreover

the metering signal is ramped at the beginningand

at the end of each pulse to prevent undesirableclic-

king noise ; the slope is determined by the value of

CINT (see the external component list of L3030).

The SLIC also provides, in the transmit direction

(from line to 4-wire side), an amplifier to insert an ex-

ternal notch filter (series resonator) for suppressing

the 12/16kHz residual signal.

Fig. 4 shows a suggestednotch Filter configuration.

The metering pulses can be injected with a DC line

current equal to zero (ON-HOOK Operation).

If teletax is not used the notch filter can be replaced

by a 1K

Ω resistor.

Inconversationmode theAC impedanceat the lineter-

minals,ZML,issynthetizedbytheexternalcomponents

ZAC and RP, according to the following formula :

ZML = ZAC + (RP1 + RP2)

Dependingon the characteristic of the ZAC network,

ZML can be either a pure resistance or a complex im-

pedance,soallowing ST SLICtomeetdifferentstand-

ards as far as the return loss is concerned. The

capacitor CCOMP guaranteesstability to the system.

The two-to-four wire conversion is achieved by me-

ans of a Wheatstone bridge configuration,the sides

of which being :

1) the line impedance (Zline),

2) the SLIC impedance at line terminals (ZML),

3) thenetworkZA connectedbetweenpin 36 and 41

of L3030 (see external component list of L3030),

4) the network ZB between pin 36 and ground that

shall copy the line impedance.

For a perfectbalancing, the following equationshall

be verified :

ZML

Zline

It is important to underline that ZA and ZB are not

obliged to be equal to ZML and to Zline, but they

both may be multiplied by a factor (up to ten) so al-

lowing use of smaller capacitors.

Inconversation,the L3000Sdissipatesabout250mW

foritsownoperation; thedissipationdependingon the

current supplied to the line shall be added.

The fig 5 and fig 6 show the DC characteristicfor two

different Feeding resistance.

2 x 200 Ohm and 2 x 400 respectively.

π √

LxC

R2 x

R4 xR5

xC2

Figure 4 : External Teletaxe Filter.

Figure 3 : DC Characteristic (b.b.)

ILIM = 25/30/45/70mA.

L3000S - L3030

9/29

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