pbl385701sot ETC-unknow, pbl385701sot Datasheet - Page 10

• Manufacturer Part Number: pbl385701sot
• Description: Universal Speech Circuit
• Manufacturer: ETC-unknow

Mute function
Sinking current from this pin will cut off the
gain in the
(attenuation min. 60dB) and decrease the
gain in the receiver amplifier to reach the
confidence tone level at DTMF-dialling.
The receiver mute is 40dB down from the
unmuted value to satisfy those who keep
the handset close to the ear at dialling.
the ear the confidence tone level is too low.
To alter the level, a signal can be taken
from DTMF generator output to receiver
input before the capacitor C6. The added
impedance to this point will hardly disturbe
the signal condition in active speech mode.
The microphone amplifier only, can be
muted by sinking current from the output
pin 11. See fig.4 or 9.
is used to other tasks than muting the
speech circuit it has to be isolated. If a
diode is used it has to be a low voltage drop
type. The input at mute has to be below
300mV. If the mute signal has reverse
polarity out of the system it can be phase
changed like in e.) In case it is required to
mute the receiver only, d.) it can be done
by shorting the receiver input to ground
before or after the input capacitor. Shorting
the input pin to ground (does not have to be
absolute ground) actuates a mute by driving
the amplifier into saturation thus blocking
the signal path and rendering a mute with
high attenuation but will cause a DC-level
shift at output which in its turn will cause a
”click ” in the earphone. This can be softe-
PBL 385 70
10
Figure 15. Mute principles.
The circuit has a mute function at pin 5.
Optional conditions.
For users who keep the handset from
Figure 15 b.) If the system mute signal
Mute
V
Mute
I
Mute
a)
microphone amplifier
5
385 70
PBL
14
-L
Mute
The diode has to be low
voltage drop type.
V
I
Mute
Mute
ned with a slower mute signal flank. If the
second approach, grounding before the
input capacitor is chosen, the grounding
has to be low ohmic in order to render a
high attenuating mute.
Start up circuit
which function is to fast charge the
capacitor C1 when the circuit goes into
hook- off condition. The fast charge circuit
is a thyristor function between pins 1 and
4 that will stop conducting when the current
drain at pin 4 is lower than 700 A + the
internal current consumption. ( about 1
mA) This circuit can not retrigger before
the voltage level at C1 drops below 2V or
the line voltage below 1V. See fig 16.
Figure 16. Fast start up principle.
b)
The circuit contains a start up device
Tx
1
2
5
385 70
PBL
14
PBL 385 70
-L
DC supply
4
c)
-L
14
R3
C1
5
+Line
-Line
385 70
PBL
Power supplies DC1, DC2, V +C and
V PA
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
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).
resistance value of R3. 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 to the
impedance specification towards the line.
The speech circuit sinks 1mA into pin 4,
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 4 that has become
too low. It is obvious that this problem is
also connected into what kind of DC-
characteristic is set. See fig. 7.
PBL 38570 generates its own DC supply
Care has to be taken when deciding the
Mute
(See fig.17)
Muting
points
Receiver mute only.
d)
15
385 70
PBL
Rx
18
17