L3037FN datasheet(5/22 Pages) STMICROELECTRONICS

5 / 22 page

DESCRIPTION (continued)

One special selection with high longitudinal balan-

ce performances allows to meet the United States

BELLCORE requirements for central office/loop

carrier and private applications.

The SLIC integrates loop start, ground start,

ground key on/off-hook, automatic ring-trip as well

as zero crossing ring relay driver.

Two to four wire conversion is implemented by the

SLIC for application with first generation COMBO.

In case of application with second generation (pro-

grammable) COMBO this function can be imple-

mented outside saving external components.

The L3037 offers programmable current limitation

(3 ranges), on hook transmission and low power

in all operating modes, power management is

controlled by a simple external low cost transistor.

Metering pulses are injected on the line via a sum-

ming node through TTXIN pin.

Metering pulse filtering is performed by means of a

simple RC network with standard tolerance compo-

nents. In case TTX function is not used this pin

must be connected to AGND. It is also possible to

use this pin to modify the DC voltage drop between

TIP/RING terminals and battery voltage for appica-

tions where it is important to optimize the battery

voltage supply versus the signal swing.

Effect of protection resistors mismatch are com-

pensated by a feedback loop on the final stage al-

lowing good long balance performances also with

large tolerance protection resistors (ex: PTC).

This function allow the L3037 to be fully conform

to BELLCORE power cross and surge test and

meet also the Longitudinal Balance Specification

without using matched PTC resistors.

An integrated thermal protection circuit forces the

L3037 in POWER DOWN (PD) mode when the

junction temperature exceeds 150

°C Typ.

The L3037 is specified over -40

°C to +85°Cam-

bient temperature range.

The L3037 package is a surface mount PLCC44

or PQFP44.

FUNCTIONAL DESCRIPTION

L3037 is designed in 70V bipolar technology and

performs the telephone line interface functions re-

quired in both C.O. and PABX environments. The

full range of signal transmission, battery feed,

loop supervision are performed.

Signal transmission performance is compatible

with European and North American Standards

and with CCITT recommendations.

Ringing, overvoltage and power cross protection

are performed by means of external networks.

The signal transmission function includes both 2

to 4 wire and 4 to 2 wire conversion. The 2W ter-

mination impedance is set by means of an exter-

nal impedance which may be complex. The 2 to 4

wire conversion is provided by means of an exter-

nal network.

Such a network can be avoided in case of appli-

cations with COMBOII, in this case the 2 to 4 wire

conversion is implemented inside the COMBOII

by means of the programmable Hybal filter.

An additional input allows a metering pulse signal

to be added on the line.

The DC feed resistance is programmable with

one external resistor. Three different values of

current limitation (25, 44, 55mA)can be selected

by software through the parallel digital interface.

One external transistor reduces the power dissi-

pation inside the L3037 in the presence of a short

loop (limiting current region).

An additional supervisory function sets the TIP

lead into high impedance state in order to allow

application in ground start configurations.

The different L3037 operating modes are control-

led by a 4bit logic interface, two additional detec-

tor outputs provide ground key detection and ei-

ther hook state or ring trip detection.

SLIC OPERATING MODES

Through the L3037 digital interface it is possible

to select 5 different SLIC operating modes:

1) Active Mode (ACT)

2) Standby Mode (SBY)

3) Tip Open Mode (TO)

4) Power Down Mode (PD)

5) Ringing Mode (RNG)

In both ACT and SBY modes it is possible to se-

lect the reverse polarity (see control interface).

Transition from direct to reverse polarity is soft

and the transition time is defined by the external

capacitor CREV.

ACTIVE MODE (ACT)

This operating mode is set by the card controller

when the Off-Hook condition has been recognized.

When this operating mode is selected the two out-

put buffers (TIP/RING) can sink or source up to

100mA each. In case of Ground key or line termi-

nals to GND the output current is limited to 15mA

for the Tip wire and 30mA for the Ring wire.

As far as the DC characteristic is concerned three

different feeding conditions are present:

a) Current limiting region: the DC impedance of

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

system works like a current source. Using the

L3037 digital interface it is possible to select the

value of the limiting current:

25mA, 44mA, or 55mA.

When the device is in limiting current region the

negative supply for the output buffer is fixed by

L3037

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