L3000S Просмотр технического описания (PDF) - STMicroelectronics

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L3000S

SUBSCRIBER LINE INTERFACE KIT

STMicroelectronics 

L3000S - L3030

The AC characteristic is just the resistance of the

two serial resistors RP.

In Stand-bymode the batterypolarity is just in direct

condition,that is the TIP wire more positive than the

RING one ; boost battery is not achievable. There

are two possible line conditions where the SLIC is

expected to be in stand-by mode :

1) ON-HOOK (Iline < 5mA). Normal on-hook

condition.

2) OFF-HOOK (Iline > 7mA). Handset is unhooked,

the SLIC is waiting for command to activate

conversation.

When the SLIC is in stand-by mode, the power dis-

sipation of L3000S does not exceed 120mW (from

-48V) eventually increased of a certain amount if

some current is flowing into the line.

The power dissipation of L3030 in the same condi-

tion, is typically 120mW.

The Stand-byMode is set when the byte sent to the

L3030 Serial Digital Interface has the first two bits

(BIT0R and BIT1R) equal to ”0”.

Settingto 0 all the 8 bits of the command sent to the

digital interface of L3030, the bias currents of both

L3000S and L3030 are reduced and only some

parts of the two circuits are active similarly to the

stand-by mode ; in this situation, named power-

down denial, the line sensors are disabled

(ON/OFF-HOOK line conditions cannot be recogni-

zed) and the current supplied to the line is limited at

0.25mA.

Conversation (CVS) or Active Mode

In conversationmodeit is possibleto selectbetween

two different DC Characteristics by the BIT5R of the

Serial Interface.

1) Normal Battery (NB)

2) Boost Battery (BB)

It is also possibleto select(BIT4R)the polarity of the

DC line voltage and (BIT6R-BIT7R) one of the four

values of limiting current (25mA or 30mA or 45mA

or 70mA).

Battery reverse can take place either before or du-

ring conversation.

As far as the DC characteristic in Normal Battery is

concerned, three different feeding conditions are

present :

a) current limiting region ; the DC impedance of the

SLIC is very high (> 20 Kohm) and therefore the

systemworkslike a currentgenerator,the current

value being set through the digital interface

(25/30/45/70mA).

b) standard feeding system region ; the

characteristic is equal to a – 48V (– 60V) battery

(note 1), in series with two resistors, whose value

is set by external components (see external

component list of L3030).

c) low impedance region ; the battery value is

reducedto 33V (45V) and the serial resistance is

reduced to the value specified in stand by mode,

that

is

:

2

3

x

(RFS

+

2RP)

Switching betweenthe three region is automaticwi-

thout discontinuity, and depends on the loop resi-

stance.Fig. 2 shows the DC characteristic in normal

battery condition.

Whenthe boostbatteryconditionisactivatedthe low

impedance region can never be reached by the sy-

Figure 2 : DC Characteristic (n.b.) ILIM = 25/30/45/70mA.

Note :

8/29

1. This value of voltage battery, named apparent battery, is fixed internally by the control unit and is independent of the actual battery

value. So, the voltage drop in the low impedance region is 15V. It is also possible to increase up to 25V this value setting BIT3R to 1.

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