PBL 386 20/2
7
6
5
4
3
2
1
0
0
10
20
30
40
50
60
ROV (kΩ)
Figure 11. Programmable overhead voltage (POV). RL = 600 Ω or ∞.
is energized, dc current flows and the
comparator input voltage reverses polar-
ity.
Ringing State
Relay driver
Theringrelaydriverandtheringtripdetector
are activated and the ring trip detector is
indicating off hook with a logic low level at
the detector output.
As the SLIC do not have any stand by state
the SLIC will remain in the active normal
state.
ThePBL38620/2SLIC incorporatesaring
relay driver designed as open collector
(npn) with a current sinking capability of
50 mA. The drive transistor emitter is
connected to BGND. The relay driver has
an internal zener diode clamp for inductive
kick-back voltages.Care must be taken
when using the relay driver together with
relays that have high impedance.
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
ringleadofthetwo-wireport.Thedcvoltage
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 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.
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 deter-
mine the duty cycle. When the DET output
is at logic level low for more than half the
time, off-hook condition is indicated.
Active States
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.
Theloopcurrentorthegroundkeydetector
is activated. The loop current detector is
indicatingoffhookwithalogiclowleveland
the ground key detector is indicating active
groundkeywithalogichighlevelpresentat
the detector output.
Control Inputs
The PBL 386 20/2 SLIC has three digital
control inputs, C1, C2 and C3.
AdecoderintheSLICinterpretsthecontrol
inputconditionandsetsupthecommanded
operating state.
C1 to C3 are internal pull-up inputs.
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.
13
ERICSSON [ ERICSSON ]
