pbl38571 ETC-unknow, pbl38571 Datasheet - Page 11

• Manufacturer Part Number: pbl38571
• Description: High Current Speech Line Interface Circuit
• Manufacturer: ETC-unknow

Power supply V +C.
supply V +C dependent of line current with
an internal shunt regulator. This regulator
senses the line voltage V L via R 3 and line
current via R 6 in order to set the correct
V +C so the circuit can generate the required
DC characteristic for a given line resistance
R Line and the line feeding data of the
exchange. A decoupling capacitor is
needed between pins +C and -L. The V +C
supply changes its voltage linearly with the
Figure 18. Typical standard DTMF dialling telephone application.
PBL 385 71 generates its own DC
DIALLER
CMOS
1
4
7
*
VDD
2
5
0
8
1-5M
6
9
#
3
MUTE
DTMF
GND
47 F
+
5.1V
(See fig.18)
15k
MIC.
200
200
100 F
1 F
1 F
line current. It can be used to feed an
electret microphone. Caution must be ta-
ken though not to drain too much current
out of this output because it will affect the
internal quick start circuit by locking itself
into active state. (max. permissible current
drain 700 A)
ding the resistance value of R3. See fig.6.
All resistances that are applied from +Line
to ground (-Line) will be in parallel, forming
the real impedance towards the line. This
will sometimes result in, that the ohmic
value of R3 is increased in order to comply
10
11
+
+
R2
AM
1k
8
Care has to be taken when deci-
7
R1
18k
9
22k
3
100nF
75
AT
1
2
100nF
910
PBL 385 71
560
11k
6.2k
14
11k
47nF
62k
AR
12,13
4,5,
to the impedance specification towards
the line. The speech circuit sinks
into pin 6, which means that the working
voltage for the speech function V+ will
decrease with increasing R3, thus starving
in the end the circuit of its working voltage
. This dependency is often falsely taken as
a sign of that the circuit does not work
down to the low line current specified, but
in fact it is the working voltage at pin 6 that
has become too low. It is obvious that this
problem is also connected into what kind
of DC-characteristic is set. See fig. 8.
+
+
6
15
16
47 F
C1
910
R3
100
1nF
C2
15nF
15V
1W
1N4007
Hook
switch
1N4007
PBL 385 71
1N4007
1N4007
10
Teleph
line
1mA
11