PBL 386 50/2
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
R
The PBL 386 50/2 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
adjusted. Please, refer to the program-
mable CODEC/filter data sheets for
design information.
TX
VTX
V
T
PBL
386 50/2
Z
Z
Combination
CODEC/Filter
V
T
B
Z
RX
RX
RSN
Figure 10. Hybrid function.
Longitudinal Impedance
A feed back loop counteracts longitudi-
nal voltages at the two-wire port by
injecting longitudinal currents in opposing
phase.
AC - DC Separation Capacitor, CHP
ance) forms the total two wire output
impedance of the SLIC. The choise of
these programmable components have
an influence on the power supply
The high pass filter capacitor con-
nected between terminals HP and TIPX
provides the separation of the ac signal
from the dc part. CHP positions the low
end 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.
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
20Ω to longitudinal disturbances. It
should be noted that longitudinal currents
may exceed the dc loop current without
disturbing the vf transmission.
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 on CLP for different
feeding characteristics. Typical values of
the transversal to longitudinal 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 con-
nected 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.
RFeed
RSG
CLP
T-L bal. CHP
@200Hz
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 filtering.
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
[Ω]
2·50
2·200 60.4
2·400 147
2·800 301
[kΩ]
0
[nF] [dB]
[nF]
47
150
100
47
-46
-46
-43
-36
150
150
150
22
Table 1. RSG , CLP and CHP values for
different feeding characteristics.
Capacitor CLP
The capacitor CLP, which connects
between the terminals CLP and VBAT,
positions together with the resistive loop
feed resistor 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 with RSG, CHP
and ZT (see section Two-Wire Imped-
1/(2·π·f·CRC).
11
ERICSSON [ ERICSSON ]
