PBL386151 Ericsson, PBL386151 Datasheet - Page 12

• Manufacturer Part Number: PBL386151
• Description: Subscriber Line Interface Circuit
• Manufacturer: Ericsson

PBL 386 15/1
12
High-Pass Transmit Filter
When CODEC/filter with a single 5 V power
supply is used, it is necessary to separate
the different signal reference voltages be-
tween the SLIC and the CODEC/filter. In
the transmit direction this can be done by
connecting a capacitor between the VTX
output of the SLIC and the CODEC/filter
input. This capacitor will also form, togeth-
er with R
the 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 fast enough response for the dc steps
that may occur with DTMF signaling.
Capacitor C
The capacitor C
the terminals LP and VBAT2, positions the
high end frequency break point of the low
pass filter in the dc loop in the SLIC. C
together with C
Wire Impedance) forms the total two wire
output impedance of the SLIC.
Table 1. C
Adaptive Overhead Voltage, AOV
The Adaptive Overhead Voltage feature
minimizes the power dissipation and at the
same time provides a flexible solution for
different system requirements and possi-
ble future changes concerning voice, me-
tering and other signal levels. This is done
by using an overhead voltage which auto-
matically adapts to the signal level (voice +
metering).
The PBL38615/1 will behave as a SLIC
with fixed overhead for signals in the 0-
20kHz range and with an amplitude less
than 1V
1V
function will expand the overhead voltage
making it possible for the signal to propa-
gate through the SLIC without distortion (
This is the total sum of voice and metering
signal). The expansion of the overhead
occurs instantaneously. When the signal
amplitude decreases, the overhead returns
to its initial value with a time constant of
approximately one second (see figure 11).
R
[ ]
2
•
FEED
25
Peak
and 2.5V
peak
TX
LP
. For signal amplitudes between
C
[nF]
470
and/or the input impedance of
LP
and C
LP
HP
LP
Peak
, which connects between
and Z
HP
the adaptive overhead
C
[nF]
68
values.
HP
T
(see section Two-
LP
tive overhead function will not effect the
SLIC performance in the constant current
region of operation (see figure 11). If,
however, the SLIC is in the off-hook,
constant voltage region of operation then
the influence of the adaptive headroom will
be apparent as a slight decrease in line
voltage (and hence line current) as the
SLIC adjusts to accommodate the larger
(voice + metering) signal.
Line Feed
If V
C in figure 17). the PBL 386 15/1 SLIC will
emulate constant current feed. (references
A-C in figure 17). The constant current
region is adjustable between 18 mA and 30
mA.
formula C in figure 17). the PBL 38615/1
SLIC will emulate a constant voltage feed
with 2 x 25
ences C-E in figure 17). This section is
made as steep as possible to switch battery
faster.
the SLIC will automatically switch to supply
the DC feed via Vbat rather than Vbat2
(references E in figure 17). This will not give
any disturbances on the line.
Figure 11. The AOV funktion when the AOV-pin is left open. (Observe, burst
undersampled).
During operation the influence of the adap-
If V
If the loop current is less than 5.5mA then
TR
< | VBAT2 | -5.7 approx (See formula
TR
> | VBAT2 | -5.7 approx (See
source impedance (refer-
2.50 V
2.50 V
1 V
Peak
2.50 V
between the TIPX and RINGX terminals
tracks the battery voltage VBAT(references
J in figure 17). According to the formula:
open loop conditions (references G in figure
17) the overhead voltage is reduced. The
line voltage is kept nearly constant with a
steep slope corresponding to 2x25
(references H in figure 17), to ensure
maximum open loop voltage, even with a
leaking telephone line.
Constant Current Region
figure 17) is adjusted by connecting a resis-
tor, R
according to the equation:
The open loop voltage, V
When the line current is approaching
The constant current (reference A-C in
R
Can simplifies to:
R
V
LC
LC
TRMAX
LC
=
=
, between terminal PLC and ground
I
I
500
500
LProg
LProg
= | VBAT | -4.6
-
10.4
•
In (I
I
LProg
LProg
TRMAX
•
32)
, measured