l3037 STMicroelectronics, l3037 Datasheet - Page 5

• Manufacturer Part Number: l3037
• Description: Subscriber Line Interface Circuit
• Manufacturer: STMicroelectronics

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 C am-
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:
When the device is in limiting current region the
negative supply for the output buffer is fixed by
25mA, 44mA, or 55mA.
L3037
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