PBL 386 30/1
VTX
PBL386 30/1
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- examined by a software routine to deter-
ity change at the comparator input when mine the duty cycle. When the DET output
the line goes off-hook. In the on-hook state is at logic level low for more than half the
no dc current flows through the loop and time, off-hook condition is indicated.
the voltage at comparator input DT is more
Ringing State
Theringrelaydriverandtheringtripdetector
are activated and the ring trip detector is
indicating off hook with a logic low level at
the detector output.
positivethanthevoltageatinputDR. When Relay driver
The SLIC is in the active normal state.
the line goes off-hook, while the ring relay
The PBL 386 30/1 SLIC incorporates a ring
Active State
is energized, dc current flows and the
relay driver designed as open collector
comparatorinputvoltagereversespolarity.
(npn) with a current sinking capability of 50
TIPX is the terminal closest to ground and
sources loop current while RINGX is the
more negative terminal and sinks loop
current. Vf signal transmission is normal
and the loop current detector is activated.
The loop current detector is indicating off
hook with a logic low level present at the
detector output.
Figure 11 gives an example of a ring trip
mA. The drive transistor emitter is
detection network. This network is
connected to BGND. The relay driver has
applicable, when the ring voltage is
an internal zener diode clamp for inductive
superimposed on VB and is injected on the
kick-back voltages. Care must be taken
ringleadofthetwo-wireport.Thedcvoltage
when using the relay driver together with
across sense resistor RRT is monitored by
relays that have high impedance.
the ring trip comparator input DT and DR
via the network R1, R2, R3, R4, C1 and C2.
With the line on-hook (no dc current) DT is
The PBL 386 30/1 SLIC have two digital
more positive than DR and the DET output
will report logic level high, i.e. the detector
A decoder in the SLIC interprets the
is not tripped. When the line goes off-hook,
while ringing, a dc current will flow through
the loop including sense resistor RRT and
will cause input DT to become more
negative than input DR. This changes out-
put DET to logic level low, i.e. tripped
detector condition. The system controller
(or line card processor) responds by de-
energizing the ring relay, i.e. ring trip.
Control Inputs
Overvoltage Protection
The PBL 386 30/1 SLIC must be protected
against overvoltages on the telephone line
control inputs, C1 and C2.
control input condition and sets up the caused by lightning, ac power contact and
commanded operating state.
C1 and C2 are internal pull-up inputs.
induction.RefertoMaximumRatings,TIPX
and RINGX terminals, for maximum
allowablecontinuousandtransientcurrents
that may be applied to the SLIC.
Open Circuit State
In the Open Circuit State the TIPX and
RINGXlinedriveamplifiersaswellasother
circuit blocks are powered down. This
causes the SLIC to present a high
impedance to the line. Power dissipation is
at a minimum and no detectors are active.
Complete filtering of the 20 Hz ac
component at terminal DT and DR is not
necessary. A toggling DET output can be
4-207
ERICSSON [ ERICSSON ]
