PBL 386 61/2
Preliminary
High-Pass Transmit Filter
WhenCODEC/filterwithasingel5Vpower
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 RTX and/or the input impedance of
theCODEC/filter, ahigh-passRCfilter. Itis
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 CLP
ThecapacitorCLP,whichconnectsbetween
the terminals LP and VBAT, positions the
high end frequency break point of the low
pass filter in the dc loop in the SLIC. CLP
Figure 11. The AOV funktion when the AOV-pin is left open. (Observe, burst
undersampled).
together with CHP and ZT (see section Two- tude less than 3.1VPeak11. For signal ampli-
Wire Impedance) forms the total two wire tudes between 3.1VPeak and 6.2VPeak, the
∆IL = | (Vt - 3.1(11))/(RL + RFeed) |.
This reduction of line current will intro-
output impedance of the SLIC. The choice AOV-function will expand the overhead duce a transversal signal into the two-wire
of these programming components influ- voltagemakingitpossibleforthesignal, Vt, which under some circumstances may be
ence the power supply rejection ratio to propagate through the SLIC without dis- audible (e g when sending metering sig-
(PSRR) from VBAT to the two wire side in tortion (see figure 11). The expansion of nals > 3.1 VPeak without any speech signal
the low frequency range.
the overhead voltage occurs instantane- burying the transversal signal generated
ously. When the signal amplitude decreas- from the linecurrent reduction).
RFeed
[Ω]
RSG
CLP
CHP
es,theoverheadvoltagereturnstoitsinitial
valuewithatimeconstantofapproximately 6.2 VPeak
one second.
IftheAOV-pinisconnectedtoAGND, the
overhead voltage will automatically be ad-
justed for signal levels between 0.6 VPeak
The sum of all signals should not exceed
[kΩ] [nF] [nF]
4.02 330 68
23.7 330 68
147 100 33
301 47
619 22
.
2•25
2•50
2•200
2•400
2•800
Line Feed
If VTR < VApp - (ILConst • RFeed), the PBL 386 61/
2 SLIC will emulate constant current feed
(references A-C in figure 13).
33
33
and 6.2 VPeak
.
Table 1. RSG, CLP and CHP values for
different feeding characteristics.
For VTR > VApp - (ILConst • RFeed) the PBL 386
61/2 SLIC will emulate resistive loop feed
programmablebetween2•25Ω12 and2•900
Ω (references D in figure 13). The current
limitation region is adjustable between
0 mA and 65 mA13.
When the line current is approaching
open loop conditions, the overhead volt-
age is reduced. To ensure maximum open
loopvoltage, evenwithtelephonelineleak-
age, this occurs at a line current of approx-
imately 5 mA (references E in figure 13).
After the overhead voltage reduction, the
line voltage is kept nearly constant with a
steep slope corresponding to 2 • 25 Ω(ref-
erence G in figure 13).
AOV In the Constant Current Region
Whentheoverheadvoltageisautomatical-
Table 1 suggest values of CLP and CHP for
different feeding characteristics.
For values outside table 1, please con-
tact Ericsson Microelectronics for assist-
ance.
ly increased, the apparent battery (VApp
,
reference F in figure 13), will be reduced by
the signal amplitude minus 3.1 VPeak(11), (Vt
- 3.1(11)).
Intheconstantcurrentregionthischange
will not affect the line current as long as
VTR < VApp - (ILConst • RFeed) - (Vt-3.1(11)),
(references A-C in figure 13).
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 61/2 will behave as a SLIC with
fixed overhead voltage for signals in the 0
-20kHzfrequencyrangeandwithanampli-
AOV In the Resistive Loop Feed Region
Thesaturationguardwillbeactivatedwhen
the SLIC is working in the resistive loop
feed region, i.e.
The open loop voltage, VTRMax, measured
between the TIPX and RINGX terminals is
tracking the battery voltage VBat (referenc-
es H in figure 13). VTRMax is programmable
by connecting the AOV-pin to AGND or by
VTR > VApp - (ILConst • RFeed) - (Vt - 3.1(11)
(references D in figure 13).
)
If the signal amplitude is greater than
11
3.1VPeak the line current, IL, will be re-
duced corresponding to the formula
12
ERICSSON [ ERICSSON ]
