PBL 386 21/2
switching occurs when the line voltage
passes the value
Loop Monitoring Functions
Programmable overhead voltage(POV)
The loop current, ground key and ring trip
detectorsreporttheirstatusthroughacom-
mon output, DET. The detector to be
connected to DET is selected via the three
bit wide control interface C1, C2 and C3.
Please refer to section Control Inputs for a
description of the control interface.
With the POV function the overhead
voltage can be increased.
|VB2| - 40 · IL - VTRO = 3.6
For correct functionality it is important to
connect the terminal VBAT2 to the second
powersupplyviathediodeDVB2 infigure11.
An optional diode DBB connected between
terminalVBandtheVB2powersupply,see
figure 11, will make sure that the SLIC
continues to work on the second battery
even if the first battery voltage disappears.
If a second battery voltage is not used,
VBAT2 is connected to VBAT on the SLIC
and CVB2, DBB and DVB2 are removed.
If the POV pin is left open the overhead
voltage is internally set to 1.1 VPeak. The
overhead voltage is equal in on-hook and
off-hook. If a resistor ROV is connected
between the POV pin and AGND, the
overhead voltage can be set to higher
values, typical values can be seen in
figure 10. The ROV and corresponding
VTRO (signal headroom) are typical values
for THD <1% and the signal frequency
1000Hz.
Observe that the 4-wire output terminal VTX
cannothandlemorethan3.2VPeak. Soifthe
gain 2-wire to 4-wire is 0dB, 3.2 VPeak is
maximum also for the 2-wire side. Signal
levels between 3.2 and 6.4 VPeak on the
2-wire side can be handled with the PTG
shorted so that the gain G2-4S become
-6.02dB. Please note that the 2-wire
impedance, RR and the 4-wire to 4-wire
gain has to be recalculated if the PTG is
shorted.
Loop Current Detector
The loop current detector is indicating that
the telephone is off hook and that current is
flowing in the loop by putting the output
DET to a logical low level when selected.
The loop current threshold value, ILTh, at
which the loop current detector changes
state is programmable by selecting the
valueofresistorRLD.RLD connectsbetween
pin PLD and ground and is calculated
according to
CODEC Receive Interface
The PBL 386 21/2 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 receive output
viatheresistorRRX,isdcbiasedwith+1.25V.
This makes it possible to compensate for
currents floating due to dc voltage
differences between RSN and the CODEC
outputwithoutusinganycapacitors. Thisis
done by connecting a resistor RR between
the RSN terminal and ground. With current
directions defined as in figure 13, current
summation gives:
500
RLD
=
ILTh
The current detector is internally filtered
and is not influenced by the ac signal at the
two wire side.
Please note that the maximum signal
current at the 2-wire side can not be
greater than 9 mA.
Ground Key Detector
How to use POV:
The ground key detector is indicating when
thegroundkeyispressed(active)byputting
the output pin DET to a logical high level
when selected. The ground key detector
circuit senses the difference in TIPX and
RINGX currents. When the current at the
RINGX side exceeds the current at the
TIPX side with the threshold value the
detector is triggered. For threshold current
values, please refer to the datasheet.
1.
Decide what overhead
voltage(VTRO) is needed. The POV
function is only needed if the
overhead voltage exceeds 1.1 VPeak
In figure 10 the corresponding ROV
for the decided VTRO can be found.
If the overhead voltage exceeds
3.2 VPeak, the G2-4S gain has to be
changed to -6.02dB by connecting
the PTG pin to AGND. Please note
that the 2-wire impedance, RR and
the 4-wire to 4-wire gain has to be
recalculated.
−IRSN = IRT + IRRX + IRR
=
2.
3.
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
calculated as
Ring Trip Detector
Ring trip detection is accomplished by
connecting an external network to a
comparator in the SLIC with inputs DT and
DR. The ringing source can be balanced or
unbalanced superimposed on VB or GND.
The unbalanced ringing source may be
applied to either the ring lead or the tip lead
with return via the other wire. A ring relay
drivenbytheSLICringrelaydriverconnects
the ringing source to tip and ring.
The ring trip function is based on a polarity
change at the comparator input when the
line goes off-hook. In the on-hook state no
dc current flows through the loop and the
voltage at comparator input DT is more
positivethanthevoltageatinputDR. When
the line goes off-hook, while the ring relay
1,25
RR
=
1,25 − VCODEC
1,25
RT
Analog Temperature Guard
−IRSN
−
−
RRX
The widely varying environmental
conditions in which SLICs operate may
lead to the chip temperature limitations
being exceeded. The PBL 386 21/2 SLIC
reduce the dc line current when the chip
temperaturereachesapproximately145°C
and increases it again automatically when
the temperature drops. Accordingly trans-
mission is not lost under high ambient
temperature conditions.
For the value on IRSN, see table 3.
The resistor RR has no influence on the ac
transmission.
SLIC
IRSN [µA]
PBL 386 21/2
-55
Table3. TheSLICinternalbiascurrentwith
the direction of the current defined as
positivewhenfloatingintotheterminalRSN.
The detector output, DET, is forced to a
logic low level when the temperature guard
is active.
12
ERICSSON [ ERICSSON ]
