L3000S 查看數據表（PDF） - STMicroelectronics

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L3000S

SUBSCRIBER LINE INTERFACE KIT

STMicroelectronics 

L3000S - L3030

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 controlproces-

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

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

12kHz(or16kHz)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

(fromline to 4-wire side), an amplifier to insert anex-

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 1KΩ resistor.

Inconversationmode theAC impedanceatthe lineter-

minals, ZML, is synthetizedby theexternalcomponents

ZAC and RP, according to the following formula :

ZML = ZAC + (RP1 + RP2)

Dependingon the characteristic of the ZAC network,

ZML canbe eithera pure resistance or a complex im-

pedance,soallowing ST SLICtomeetdifferentstand-

ards as far as the return loss is concerned. The

capacitorCCOMP 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 36and 41

of L3030 (see externalcomponentlist 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 :

ZA

ZB

=

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; thedissipationdependingonthe

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.

Figure 3 : DC Characteristic (b.b.)

ILIM = 25/30/45/70mA.

Figure 4 : ExternalTeletaxe Filter.

f= 1

2π √LxC

L

=

R2

x

R4

R3

xR5

xC2

9/29

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