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参数资料
| 型号： | PBL386652QNT |
| 厂商： | ERICSSON |
| 英文描述： | Subscriber Line Interface Circuit |
| 中文描述： | 用户线接口电路 |
| 文件页数： | 12/18页 |
| 文件大小： | 184K |
| 代理商： | PBL386652QNT |
PBL 386 65/2
12
Preliminary
High-Pass Transmit Filter
When CODEC/filter with a singel 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
and/or the input impedance of
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
LP
The capacitor C
, which connects between
the terminals LP and VBAT, positions the
high end frequency break point of the low
pass filter in the dc loop in the SLIC. C
LP
together with C
and Z
(see section Two-
Wire Impedance) forms the total two wire
output impedance of the SLIC. The choice
of these programming components influ-
ence the power supply rejection ratio
(PSRR) from VBAT to the two wire side in
the low frequency range.
R
Feed
[
2
25
2
50
2
200
2
400
2
800
Table 1. R
, C
and C
values for
different feeding characteristics.
R
SG
[k
]
4.02
23.7
147
301
619
C
[nF]
330
330
100
47
22
C
[nF]
68
68
33
33
33
Table 1 suggest values of C
and C
HP
for
different feeding characteristics.
Adaptive Overhead Voltage, AOV
The Adaptive Overhead Voltage feature
minimises the power dissipation and at the
same time provides a flexible solution for
differing 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). With the AOV-pin left open, the
PBL 386 65/2 will behave as a SLIC with
fixed overhead voltage for signals in the 0
- 20kHz frequency range and with an ampli-
tude less than 3.1V
Peak11
. For signal ampli-
tudes between 3.1V
and 6.2V
, the
AOV-function will expand the overhead
voltage making it possible for the signal, Vt,
to propagate through the SLIC without dis-
tortion (see figure 11). The expansion of
the overhead voltage occurs instantane-
ously. When the signal amplitude decreas-
es, the overhead voltage returns to its initial
value with a time constant of approximately
one second.
If the AOV-pin is connected to AGND, the
overhead voltage will automatically be ad-
justed for signal levels between 0.6 V
Peak
and 6.2 V
Peak
.
AOV In the Constant Current Region
When the overhead voltage is automatical-
ly increased, the apparent battery (V
,
reference F in figure 15), will be reduced by
the signal amplitude minus 3.1 V
Peak(11)
,
(Vt - 3.1
(11)
).
In the constant current region this change
will not affect the line current as long as
V
< V
- (I
R
) - (Vt-3.1
(11)
),
(references A-C in figure 15).
AOV In the Resistive Loop Feed Region
The saturation guard will be activated when
the SLIC is working in the resistive loop
feed region, i.e.
V
> V
- (I
R
) - (Vt - 3.1
(11)
)
(references D in figure 15).
If the signal amplitude is greater than
3.1V
Peak11
the line current, I
, will be re-
duced corresponding to the formula
I
= | (Vt - 3.1
(11)
)/(R
+ R
) |.
This reduction of line current will intro-
duce a transversal signal into the two-wire
which under some circumstances may be
audible (e g when sending metering sig-
nals > 3.1 V
without any speech signal
burying the transversal signal generated
from the linecurrent reduction).
The sum of all signals should not exceed
6.2 V
Peak
.
Line Feed
If V
< V
- (I
R
), the PBL 386 65/
2 SLIC will emulate constant current feed
(references A-C in figure 15).
For V
> V
- (I
R
) the PBL 386
65/2 SLIC will emulate resistive loop feed
programmable between 2
25
12
and 2
900
(references D in figure 15). The current
limitation region is adjustable between 0
mA and 65 mA
13
.
When the line current is approaching
open loop conditions, the overhead volt-
age is reduced. To ensure maximum open
loop voltage, even with telephone line leak-
age, this occurs at a line current of approx-
imately 5 mA (references E in figure 15).
After the overhead voltage reduction, the
line voltage is kept nearly constant with a
steep slope corresponding to 2
25
(ref-
erence G in figure 15).
The open loop voltage, V
, measured
between the TIPX and RINGX terminals is
tracking the battery voltage V
(referenc-
es H in figure 15). V
is programmable
by connecting the AOV-pin to AGND or by
leaving the AOV-pin open.
Figure 11. The AOV funktion when the AOV-pin is left open. (Observe, burst
undersampled).
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