PBL 386 50/2
gized, dc current flows and the compara-
tor input voltage reverses polarity.
Figure 12 gives an example of a ring
trip detection network. This network is
applicable, when the ring voltage is
superimposed on VB and is injected on
the ring lead of the two-wire port. The dc
voltage across sense resistor RRT is
monitored by 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 more positive than
DR and the DET output will report logic
level high, i.e. the detector 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 output DET
to logic level low, i.e. tripped detector
condition. The system controller (or line
card processor) responds by de-energiz-
ing the ring relay, i.e. ring trip.
VTX
PBL386 50/2
CODEC
DC-GND
RT
I
IRT
IRSN
IRRX
RRX
_
RSN
+
IRR
+1.25 V
UREFcodec
RR
Figure 14. CODEC receive interface.
and the programmed dc characteristic,
with the longitudinal current compensa-
tion (see section Longitudinal Imped-
ance) not active, to the line on the
RINGX pin.
Ringing State
The ring relay driver and the ring trip
detector are activated and the ring trip
detector is indicating off hook with a logic
low level at the detector output.
Complete filtering of the 20 Hz ac
component at terminal DT and DR is not
necessary. A toggling DET output can be
examined by a software routine to
determine the duty cycle. When the DET
output is at logic level low for more than
half the time, off-hook condition is
The loop current detector is active.
The SLIC is in the active normal state.
Active Polarity Reversal State
Active States
TIPX and RINGX polarity is reversed
from the Active State: RINGX is the
terminal closest to ground and sources
loop current while TIPX is the more
negative terminal and sinks current. Vf
signal transmission is normal. The loop
current or the ground key detector is
activated. The loop current detector is
indicating off hook with a logic low level
and the ground key detector is indicating
active ground key with a logic high level
present at the detector output.
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. The loop current or the ground
key detector is activated. The loop
current detector is indicating off hook
with a logic low level and the ground key
detector is indicating active ground key
with a logic high level present at the
detector output.
In PBL 386 50/2 a line voltage meas-
urement feature is available in the active
state, which may be used for line length
estimations or for line test purposes. The
line voltage is presented on the detector
output as a pulse at logic high level with
a pulsewidth of 5.5 µs/V. To start the line
voltage measurement this mode has to
be entered from the Active State with the
loop or ground key detector active. The
pulse presented at the DET output
proportional to the line voltage starts
when entering the line voltage measuring
mode.
indicated.
Relay driver
The PBL 386 50/2 SLIC incorporates a
ring relay driver designed as open
collector (npn) with a current sinking
capability of 50mA. The drive transistor
emitter is connected to BGND. The relay
driver has an internal zener diode clamp
for inductive kickback voltages. Care
must be taken when using the relay
driver together with relays that have high
impedance.
Overvoltage Protection
The PBL 386 50/2 SLIC must be
protected against overvoltages on the
telephone line caused by lightning, ac
power contact and induction. Refer to
Maximum Ratings, TIPX and RINGX
terminals, for maximum allowable
continuous and transient currents that
may be applied to the SLIC.
Control Inputs
The PBL 386 50/2 SLIC have three
digital control inputs, C1, C2 and C3.
A decoder in the SLIC interprets the
control input condition and sets up the
commanded operating state.
C1 to C3 are internal pull-up inputs.
Open Circuit State
Secondary Protection
In the Open Circuit State the TIPX and
RINGX line drive amplifiers as well as
other 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.
The circuit shown in figure 12 utilizes
series resistors together with a
programmable overvoltage protector
(e.g. PowerInnovations TISPPBL2),
serving as a secondary protection.
Tip Open State
Tip Open State is used for ground start
signalling.
In this state the SLICs present a high
impedance to the line on the TIPX pin
15
ERICSSON [ ERICSSON ]
