PBL 386 30/2
The current limit (reference C in figure
12) is adjusted by connecting a resistor,
RLC, between terminal PLC and ground
according to the equation:
tions and to fit both single and dual battery
feed CODECs. The RSN terminal, con-
necting to the CODEC 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 differ-
ences between RSN and the CODEC out-
put without using any capacitors. This is
done by connecting a resistor RR between
the RSN terminal and ground. With current
directions defined as in figure 13, current
summation gives:
Battery Feed
The PBL 386 30/2 SLIC emulate resistive
loop feed, programmable between 2·50 Ω
and 2·900 Ω, with adjustable current limita-
tion. In the current limited region the loop
current has a slight slope corresponding to
2·30 kΩ, see figure 12 reference B.
The open loop voltage measured be-
tween the TIPX and RINGX terminals is
tracking the battery voltage VBat. The sig-
1000
ILProg + 4
RLC
=
where RLC is in kΩ for ILProg in mA.
A second, lower battery voltage may be
connected to the device at terminal VBAT2
toreduceshortlooppowerdissipation. 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 > 6mA.
For correct functionality it is important to
connect the terminal VBAT2 to the second
powersupplyviathediodeDVB2 infigure11.
nallingheadroom,oroverheadvoltageVTRO
,
is programmable with a resistor ROV con-
nected between terminal POV on the SLIC
and ground. Please refer to section “Pro-
grammable overhead voltage(POV)”.
The battery voltage overhead, VOH, de-
pendsontheprogrammedsignaloverhead
voltage. VOH defines the TIP to RING volt-
age at open loop conditions according to
−IRSN = IRT + IRRX + IRR
=
1,25 1,25 − VCODEC
1,25
RR
+
+
RT
RRX
whereVCODEC isthereferencevoltageofthe
CODEC at the receive output.
From this equation the resistor RR can be
VTR(at IL = 0 mA) = |VBat| - VOH
.
Refer to table 2 for typical values on VOH
andVOHVirt.Theoverheadvoltageischanged
when the line current is approaching open
loop conditions. To ensure maximum open
loopvoltage,evenwithaleakingtelephone
line, this occurs at a line current of approxi-
mately 6 mA. When the overhead voltage
haschanged, thelinevoltageiskeptnearly
constant with a steep slope corresponding
to 2·25 Ω(reference G in figure 12).
An optional diode DBB connected be- calculated as
tween terminal VB and the VB2 power
1,25
1,25 − VCODEC
supply, see figure 11, will make sure that
the SLIC continues to work on the second
battery even if the first battery voltage dis-
appears.
RR
=
1,25
RT
−IRSN
−
−
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.
The virtual battery overhead, VOHvirt, is
defined as the difference between the bat-
tery voltage and the crossing point of all
possible resistive feeding slopes, see fig-
ure12referenceJ. Thevirtualbatteryover-
head is a theoretical constant needed to be
able to calculate the feeding characteris-
tics.
SLIC
IRSN [µA]
Metering applications
For designs with metering applications
please contact Ericsson Microelectronics
for assistance.
PBL 386 30/2
-55
CODEC Receive Interface
Table3. TheSLICinternalbiascurrentwith
the direction of the current defined as posi-
tive when floating into the terminal RSN.
The PBL 386 30/2 SLIC have got a com-
pletely new receive interface at the four
wiresidewhichmakesitpossibletoreduce
the number of capacitors in the applica-
SLIC
VOH(typ)
(V)
VOHvirt(typ)
(V)
PBL 386 30/2
3.0 +VTRO 4.9 +VTRO
7
6
5
4
3
2
1
0
Table 2. Battery overhead.
off-hook
on-hook
The resistive loop feed (reference D in
figure 12) is programmed by connecting a
resistor, RSG, between terminals PSG and
VBAT according to the equation:
RSG + 2 · 104
RFeed
=
+ 2RF
200
0
10
20
30
40
50
60
where RFeed is in Ω for RSG and RF in Ω.
R
ov
(KΩ)
Figure 10. Programmable overhead voltage (POV). RL = 600 Ω or ∞.
12
ERICSSON [ ERICSSON ]
