PBL 386 15/1
Silent Polarity Reversal
The reversal time is set by a capacitor,
Csprv, betweenthe pinSPRandAGND. The
reversal has a setup time and reversal time
see figure 14.
The setup time is different in Active- to
Reversal-stateandReversal-toActivestate
but the silent polarity reversal time is the
same Active- to Reversal-state and Rever-
sal- to Active state. To calculate the silent
polarity reversal time use following for-
mula:
tr =CSPR . 9500
Active- to Reversal-state and Reversal-
to Active state and the setup time use
following formulas.
C2 = 5 V, C1 = 0 V
C
= 4.7 µF / 6V
RLSP=R 600 Ω RFEED = 2 *25 Ω
Active → Reversal:
t
Act → Rev = CSPR . 17500
Reversal → Active:
tRev → Act = CSPR . 15500
Figure 14. Silent Polarity Reversal
The time is measured between 10%
and 90% of the line voltage. The reversal
time is independent of line load and line
current.
Loop Current Detector
Ring Trip Detector
The loop current detector indicates that
the telephone is off hook and that DC
current is flowing in the loop by putting the
output pin DET, to a logic low level when
selected. The loop current detector thresh-
old value, ILTh, where the loop current de-
tectorchangesstate,isprogrammablewith
the RLD resistor. RLD connects between pin
PLD and ground and is calculated accord-
ing to:
Ring trip detection is accomplished by
connecting an external network to a com-
parator in the SLIC with inputs DT and DR.
The ringing source can be balanced or
unbalanced e g superimposed on the bat-
tery voltage or ground. 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 driven by the SLIC
ringrelaydriverconnectstheringingsource
to tip and ring.
The ring trip function is based on a polar-
ity 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
is energized, dc current flows and the com-
parator input voltage reverses polarity.
Figure 15 gives an example of a ring trip
detection network. This network is applica-
ble, when the ring voltage superimposed
onthebatteryvoltageisinjectedonthering
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 filter network R1, R2, R3, R4, C1 and
C2. DT is more positive than DR, with the
line on-hook (no dc current). The DET
output will report logic level high, i.e. the
detector is not tripped. When the line goes
off-hook,whileringing,adccurrentwillflow
Analog Temperature Guard
The widely varying environmental
conditions in which SLICs operate may
lead to the chip temperature limitations
being exceeded. The PBL 386 15/1 SLIC
reduces the dc line current and the
longitudinal current limit when the chip
temperaturereachesapproximately145°C
and increases it again automatically when
the temperature drops.
The detector output, DET, is forced to a
logic low level when the temperature guard
is active.
The Active state temperature guard is
exclusively viewed at detector output see
section Active Temperature guard.
500
ILTh
RLD
=
Ground Key Detector
The ground key detector indicates when
the ground key is pressed (active) by put-
ting the output pin DET to a logic high level
when selected. The ground key detector
circuitsensesthedifferencebetweenTIPX
and RINGX currents. The detector is trig-
gered when the difference exceeds the
current threshold.
Loop Monitoring Functions
The loop current, ground key and ring trip
detectorsreporttheirstatusthroughacom-
mon output, DET. The status of the detec-
tor pin, DET, is selected via the three bit
control interface C1, C2 and C3. Please
refertosectionControlInputsforadescrip-
tion of the control interface.
14
ERICSSON [ ERICSSON ]
