PBL 386 50/2
The current limit (reference C in figure
13) is adjusted by connecting a resistor,
RLC, between terminal PLC and ground
according to the equation:
receive output via the resistor RRX, is dc
biased with +1.25V. This makes it
possible to compensate for currents
floating due to dc voltage differences
between RSN and the CODEC output
without using any capacitors. This is
done by connecting a resistor RR be-
tween the RSN terminal and ground.
With current directions defined as in
figure 14, current summation gives:
Battery Feed
The PBL 386 50/2 SLIC emulate
resistive loop feed, programmable
between 2·50Ω and 2·900 Ω, with
adjustable current limitation. In the
current limited region the loop current
has a slight slope corresponding to
2·30 kΩ, see figure 13 reference B.
The open loop voltage measured
between the TIPX and RINGX terminals
is tracking the battery voltage VBat. The
signalling headroom, or overhead voltage
1000
LProg + 4
RLC
=
I
where RLC is in kΩ for ILProg in mA.
A second, lower battery voltage may be
connected to the device at terminal
VBAT2 to reduce short loop power
dissipation. The SLIC automatically
switches between the two battery supply
voltages without need for external
control. The silent battery switching
occurs when the line voltage passes the
value |VB2| - 40·IL - (VOHVirt -1.3),
if IL > 6 mA.
For correct functionality it is important
to connect the terminal VBAT2 to the
second power supply via the diode DVB2
in figure 12.
An optional diode DBB connected
between terminal VB and the VB2 power
supply, see figure 12, will make sure that
the SLIC continues to work on the
second battery even if the first battery
voltage disappears.
−IRSN = IRT + IRRX + IRR
=
1,25 1,25 − VCODEC
1,25
RR
VTRO, is programmable with a resistor ROV
+
+
RT
RRX
connected between terminal POV on the
SLIC and ground. Please refer to section
“Programmable overhead voltage(POV)”.
The battery voltage overhead, VOH
depends on the programmed signal
overhead voltage VTRO. VOH defines the
TIP to RING voltage at open loop
conditions according to VTR(at IL = 0 mA)
where VCODEC is the reference voltage of
the CODEC at the receive output.
From this equation the resistor RR can be
calculated as
,
1,25
RR
=
= |VBat| - VOH
.
1,25 − VCODEC
1,25
RT
−IRSN
−
−
Refer to table 2 for typical values on
VOH and VOHVirt. The overhead voltage is
changed when the line current is ap-
proaching open loop conditions. To
ensure maximum open loop voltage,
even with a leaking telephone line, this
occurs at a line current of approximately
6 mA. When the overhead voltage has
changed, the line voltage is kept nearly
constant with a steep slope correspond-
ing to 2·25 Ω(reference G in figure 13).
The virtual battery overhead, VOHVirt, is
defined as the difference between the
battery voltage and the crossing point of
all possible resistive feeding slopes, see
figure 13 reference J. The virtual battery
overhead is a theoretical constant
RRX
For values on IRSN, see table 3.
The resistor RR has no influence on the
ac transmission.
If a second battery voltage is not used,
VBAT2 is connected to VBAT on the
SLIC and CVB2, DBB and DVB2 are removed.
SLIC
IRSN [µA]
PBL 386 50/2
-155
Metering applications
For designs with metering applications
please contact Ericsson Microelectronics
for assistance.
Table 3. The SLIC internal bias current
with the direction of the current defined
as positive when floating into the terminal
RSN.
CODEC Receive Interface
Programmable overhead voltage(POV)
The PBL 386 50/2 SLIC have got a
completely new receive interface at the
four wire side which makes it possible to
reduce the number of capacitors in the
applications and to fit both single and
dual battery feed CODECs. The RSN
terminal, connecting to the CODEC
needed to be able to calculate the
feeding characteristics.
With the POV function the overhead
voltage can be increased.
If the POV pin is left open the overhead
voltage is internally set to 3.2 VPeak in off-
SLIC
VOH(typ)
[V]
VOHVirt(typ)
[V]
PBL 386 50/2 3.0 +VTRO 4.9 +VTRO
12
11
10
9
Table 2. Battery overhead.
8
off-hook
on-hook
7
6
5
4
3
2
The resistive loop feed (reference D in
figure 13) is programmed by connecting
a resistor, RSG, between terminals PSG
and VBAT according to the equation:
1
0
RSG + 2·104
RFeed
=
+ 2RF
0
10
20
30
40
50
60
200
R
ov
(KΩ)
where RFeed is in Ω for RSG and RF in Ω.
Figure 11. Programmable overhead voltage (POV). RL = 600 Ω or ∞.
12
ERICSSON [ ERICSSON ]
