PBL 386 40/2
When choosing RTX, make sure the output
load of the VTX terminal is >20 kΩ.
If calculation of the ZB formula above
yields a balance network containing an
inductor, an alternate method is recom-
mended. Contact Ericsson Microelectron-
ics for assistance.
R
FB
The PBL 386 40/2 SLIC may also be
used together with programmable
CODEC/filters. The programmable
CODEC/filter allows for system controller
adjustment of hybrid balance to accom-
modate different line impedances without
change of hardware. In addition, the
transmit and receive gain may be ad-
justed. Please, refer to the programm-
able CODEC/filter data sheets for design
information.
R
TX
VTX
V
T
PBL
386 40/2
Z
Z
Combination
CODEC/Filter
V
T
B
Z
RX
RX
RSN
Longitudinal Impedance
A Feed back loop counteracts longitudi-
nal voltages at the two-wire port by
injecting longitudinal currents in opposing
phase.
Figure 10. Hybrid function.
Thus longitudinal disturbances will
appear as longitudinal currents and the
TIPX and RINGX terminals will experi-
ence very small longitudinal voltage
excursions, leaving metallic voltages well
within the SLIC common mode range.
The SLIC longitudinal impedance per
wire, ZLoT and ZLoR, appears as typically
20 Ω to longitudinal disturbances. It
should be noted that longitudinal currents
may exceed the dc loop current without
disturbing the vf transmission.
frequency response break point of the ac
loop in the SLIC. Refer to table 1 for
recommended values of CHP.
Example: A CHP value of 150 nF will
position the low end frequency response
3dB break point of the ac loop at 1.8 Hz
(f3dB) according to f3dB = 1/(2·π·RHP·CHP)
where RHP = 600 kΩ.
impedance of the SLIC. The choise of
these programmable components have an
influence on the power supply rejection
ratio (PSRR) from VBAT to the two wire
side at sub-audio frequencies. At these
frequencies capacitor CLP also influences
the transversal to longitudinal balance in
the SLIC. Table 1 suggests suitable values
onCLP fordifferentFeedingcharacteristics.
Typical values of the transversal to longitu-
dinal balance (T-L bal.) at 200Hz is given in
table 1 for the chosen values on CLP.
High-Pass Transmit Filter
The capacitor CTX in figure 12 connected
between the VTX output and the
CODEC/filter forms, together with RTX
and/or the input impedance of a pro-
grammable CODEC/filter, a high-pass
RC filter. It is recommended to position
the 3 dB break point of this filter between
30 and 80 Hz to get a faster response for
the dc steps that may occur at DTMF
signalling.
Capacitors CTC and CRC
The capacitors designated CTC and CRC
in figure 12, connected between TIPX
and ground as well as between RINGX
and ground, can be used for RFI filter-
ing.. The recommended value for CTC
and CRC is 2200 pF. Higher capacitance
values may be used, but care must be
taken to prevent degradation of either
longitudinal balance or return loss. CTC
and CRC contribute to a metallic imped-
ance of 1/(π·f·CTC) = 1/(π·f·CRC), a TIPX to
ground impedance of 1/(2·π·f·CTC) and a
RINGX to ground impedance of 1/
(2·π·f·CRC).
RFeed
RSG
CLP
T-L bal. CHP
@200Hz
[Ω]
[kΩ]
[nF]
[dB]
[nF]
2 50
0
150
100
47
-46
-46
-43
-36
47
2 200
2 400
2 800
60.4
147
301
150
150
150
22
Table 1. RSG , CLP and CHP values for
different Feeding characteristics.
Capacitor CLP
ThecapacitorCLP,whichconnectsbetween
the terminals CLP and VBAT, positions
together with the resistive loop feed resis-
tor RSG (see section Battery Feed), the high
end frequency break point of the low pass
filter in the dc loop in the SLIC. CLP together
withRSG, CHP andZT (seesectionTwo-Wire
Impedance) forms the total two wire output
AC - DC Separation Capacitor, CHP
The high pass filter capacitor connected
between terminals HP and TIPX provides
the separation of the ac signal from the
dc part. CHP positions the low end
11
ERICSSON [ ERICSSON ]
