PBL 386 30/2
PBL386 30/2
VTX
CODEC
DC-GND
RT
I
IRT
IRSN
IRRX
RRX
_
+
RSN
IRR
+1.25 V
UREFcodec
RR
Figure 13. CODEC receive interface.
The ring trip function is based on a polar- inedbyasoftwareroutinetodeter-minethe
ity change at the comparator input when duty cycle. When the DET output is at logic
the line goes off-hook. In the on-hook state level low for more than half the time, off-
no dc current flows through the loop and hook condition is indicated.
the voltage at comparator input DT is more
minimum and no detectors are active.
Ringing State
The ring relay driver and the ring trip detec-
torareactivatedandtheringtripdetectoris
indicating off hook with a logic low level at
the detector output.
positivethanthevoltageatinputDR. When Relay driver
the line goes off-hook, while the ring relay
The PBL 386 30/2 SLIC incorporates a
The SLIC is in the active normal state.
is energized, dc current flows and the
ring relay driver designed as open
comparatorinputvoltagereversespolarity.
collector (npn) with a current sinking
Active State
Figure 11 gives an example of a ring trip
capability of 50 mA. The drive transistor
TIPX is the terminal closest to ground and
sources loop current while RINGX is the
more negative terminal and sinks loop cur-
rent. Vf signal transmission is normal and
the loop current detector is activated. The
loop current detector is indicating off hook
withalogiclowlevel presentatthedetector
output.
detection network. This network is applica-
emitter is connected to BGND. The relay
ble, when the ring voltage is superimposed
driver has an internal zener diode clamp
on VB and is injected on the ring lead of the
for inductive kick-back voltages. Care
two-wire port. The dc voltage across sense
must be taken when using the relay
resistor RRT is monitored by the ring trip
driver together with relays that have high
comparator input DT and DR via the net-
impedance.
work R1, R2, R3, R4, C1 and C2. With the line
on-hook(nodccurrent)DTismorepositive
than DR and the DET output will report
The PBL 386 30/2 SLIC have two digital
logic level high, i.e. the detector is not
Control Inputs
Overvoltage Protection
control inputs, C1 and C2.
tripped. When the line goes off-hook, while
The PBL 386 30/2 SLIC must be protected
against overvoltages on the telephone line
caused by lightning, ac power contact and
induction.RefertoMaximumRatings,TIPX
and RINGX terminals, for maximum allow-
able continuous and transient currents that
A decoder in the SLIC interprets the
ringing, a dc current will flow through the
control input condition and sets up the
loop including sense resistor RRT and will
commanded operating state.
C1 and C2 are internal pull-up inputs.
cause input DT to become more negative
than input DR. This changes output DET to
logic level low, i.e. tripped detector condi-
Open Circuit State
tion. The system controller (or line card
In the Open Circuit State the TIPX and
processor) responds by de-energizing the
RINGXlinedriveamplifiersaswellasother
ring relay, i.e. ring trip.
circuit blocks are powered down. This
Complete filtering of the 20 Hz ac com-
causes the SLIC to present a high imped-
ponent at terminal DT and DR is not neces-
ance to the line. Power dissipation is at a
sary. A toggling DET output can be exam-
15
ERICSSON [ ERICSSON ]
