1
PBL 385 82
PBL 38582
Telephone Line interface circuit for
DECT, DAM, CT
Unisolated or Isolated
Description
PBL 38582 is a monolithic bipolar integrated circuit for use as telephone line interface in
unisolated or isolated DECT and other cordless telephone residential base stations and
in analog / digital answering machines or as second line in an unisolated DECT telephone
base station.
Transmit and receive gains are set by external components. On / Off switchable gain,
related to line, regulation for different current feeds can be set by external resistors.
Typical current feeds as 48 V, 2 200 ohm, 48 V 2 400 ohm and 60 V 2 600 ohm can
be handled. Application dependent parameters such as line balance, impedance to the
line and frequency response are set by external components. Parameters are set
independently which results in an easy adoption for various market needs.
Key Features
Minimum number of inexpensive
external components, 5 capacitors
and 4 resistors.
Current range
5 - 130 mA(DIL),
5 - 100 mA(20-pin SO)
5 - 70 mA(16-pin SO) 385 82/2
Operation voltage range
down to 2 V.
Short start-up time.
Figure 1. Functional diagram. DIP package.
18-pin plastic DIP
3
1
4
+
2
Telephone
line
1
2
14,16
1 5
1 8
1 7
RECEIVE
TRANSMIT
PBL 38582
Reference
Limiter
DC
supply
Fast start - up
6
5 ,
20-pin plastic SO
16-pin plastic SO
December 1999
PBL 38582
PBL 385 82
PBL38582
2
PBL 385 82
Figure 2. Test set up without
rectifier bridge.
Figure 3. Test set up with rectifier
bridge.
Maximum Ratings
Parameter
Symbol
Min
Max
Unit
Line voltage, t
p
= 2 s
V
L
0
18
V
Line current, continuous DIP
I
L
0
130
mA
Line current, continuous SO-20 package
I
L
0
100
mA
Line current, continuous SO-16 package
I
L
PBL 38582/2
0
70
mA
Operating temperature range
T
Amb
-40
+70
C
Storage temperature range
T
Stg
-55
+125
C
No input should be set on higher level than pin 15.(+C)
Figure 4. Circuit with external
components for test set up.
R1 = 6.2 k
R2 = 62 k
R3 = 909
R6 = 75
R14 = 10k
C1 = 68
F
C2 = 15 nF
C3 = 0.1
F
C4 = 47 nF
DIP package pinning.
Receiver
output
V
3
V
4
350
310
Transmitter
input
+
+ LINE
- LINE
ARTIFICIAL
LINE
I
L
V
2
V
1
V
L
R = 0-4k
L
0 ohm when artificial
line is used
PBL 38582
with external
components
See fig. 4
R
feed = 400
+400
600
C
E = 48.5V
C = 1
F when artificial line is used
470
F when no artificial line
5H+5H
+
+
- LINE
I
L
V
2
V
1
V
L
R = 0 - 4 k
L
PBL 38582
with external
components
See fig. 4
Receiver
output
R
feed = 400
+400
600
+
E = 50.0V
V
4
1
F
Uz= 15-16V
5H+5H
350
310
V
3
Transmitter
input
+ LINE
3
1
4
+
2
14,16
1 5
1 8
1 7
R6
R1
R2
C3
C4
C2
C1
R3
PBL 38582
Reference
Limiter
DC
supply
Fast start - up
6
R14
Transmitter
input
Receiver
output
5,
+Line
-Line
R13
3
PBL 385 82
Electrical Characteristics
At T
Amb
= + 25
C. No cable and no line rectifier unless otherwise specified.
I
L
= 100 mA is not valid for 16-pin SO package.
Parameter Ref.fig. Conditions
Min
Typ
Max
Unit
Line voltage, V
L
2
I
L
= 15 mA
3.3 3.7 4.1
V
2
I
L
= 100 mA
11
13
15
V
Transmitting gain
20 10 log (V
2
/ V
3
); 1 kHz
24
25
26
dB
Transmitting frequency 2
200 Hz to 3.4 kHz
-1
1
dB
response
Transmitter dynamic output 2
200 Hz - 3.4 kHz
1.5
V
p
2% distortion, I
L
= 20 - 100 mA
Transmitter maximum output 2
200 Hz - 3.4 kHz
3
V
p
I
L
= 0 - 100 mA, V
3
= 0 - 1 V
Transmitter output noise
2
Psof-weighting, Rel 1 V
rms
, R
L
= 0
-75
dB
Psof
Transmitter input impedance 2
1 kHz
13.5 17
20.5
kohm
pin 3
Receiving gain
20 10 log (V
4
/ V
1
); 1 kHz
Without gain regulation
2
R
L
= 0 - xxx ohm, R11= 10k
-18.5
-16.5
-14.5
dB
Receiving gain
20 10 log (V
4
/ V
1
); 1 kHz, R11 not used
With gain regulation
2
R
L
= 0 ohm,
-18.5
-16.5
-14.5
dB
2
R
L
= 400 ohm
-16
-14
-12
dB
2
R
L
= 900 ohm - 2.2 kohm
-13.5
-11.5
-9.5
dB
Receiving range of regulation
2
1 kHz, R
L
= 0 to 900 ohm
3
5
7
dB
Receiving frequency response
2
200 Hz to 3.4 kHz
-1
1
dB
Receiver output impedance
2
1 kHz, without 310
resistor
3
ohm
Receiver dynamic output 2
200 Hz - 3.4 kH
0.5
V
p
note 1
2% distortion, I
L
= 20 - 100 mA
Receiver maximum output 3
Measured with line rectifier
0.9
V
p
200 Hz - 3.4 kHz,
I
L
= 0 - 100 mA, V
1
= 0 - 50 V
Receiver output noise 2
A-weighting, Rel 1V
rms
, with cable
-85
dB
A
0 - 5 km, = 0.5 mm,
0 - 3 km, = 0.3 mm
Notes:
1. The dynamic output can be nearly doubled if the 310
series resistor is omitted.
4
PBL 385 82
Pin Descriptions
Refer to figure 5.
DIP
SO 20 SO 16
Name Function
1
1
1
+L
Output of the transmitter amplifier. Connected to the line through a
polarity guard diode bridge.
2
2
2
TO
Output of the transmitter amplifier. Connected through a resistor of 47 to 100 ohm to -L.
Sets the DC-charateristic of the circuit.The output has a low AC output impedance and
the signal is used to drive a side tone balancing network.
3
3
3
TI
Input of transmit amplifier. Input impedance 17 k
20 %.
4
4
4
+C
The positive power supply terminal for most of the circuitry inside the PBL 385 82
(about 1 mA current consumption). The +C-pin is to be connected to a decoupling
capacitor of 47
F to 150
F.
6
6
6
GR
The control input for the gain regulation in the receiver.
5
5
5
14
16
12
-L
The negative power terminal, connected to the line through a polarity guard diode
16
18
14
bridge.
15
17
13
RI
Input of the receive signal amplifier. Input impedance is 38 kohm
20 %.
17
19
15
RE2
The receive signal amplifier outputs. Output impedance is approximately 3 ohm.
18
20
16
RE1
7
7
7
NA
8
8
8
NA
9
9
9
NA
10
10
10
NA
11
11
11
NA
12
12
NA
13
13
NA
14
NA
15
NA
20-pin SO
16-pin SO
18-pin DIP
Figure 5. Pin configuration.
}
}
+L
TO
TI
+C
GR
RI
-L
1
2
3
4
5
6
7
8
16
15
14
13
12
11
9
10
RE 2
RE 1
18
17
-L
NA
NA
NA
NA
NA
NA
NA
-L
1
2
3
4
5
6
7
8
20
19
18
17
16
15
14
13
TO
+L
GR
-L
RE1
NA
NA
TI
+C
RI
-L
NA
NA
NA
9
12
10
11
NA
NA
NA
NA
-L
RE2
1
2
3
4
5
6
7
8
16
14
13
TO
+L
GR
-L
NA
NA
TI
+C
RI
-L
NA
NA
NA
9
12
10
11
-L
RE2
15
RE1
5
PBL 385 82
Figure 6. AC-impedance.
Functional description
Design procedure; ref. to fig.4.
The design is made easier through that all
settable parameters are returned to gro-
und (-line), this feature differs it from bridge
type solutions.To set the parameters in the
following order will result in that the
interaction between the same is minimized.
1. Set the circuit impedance to the line,
either 600
or complex. (R3 and C1). C1
should be big enough to give low
impedance compared with R3 in the
telephone speech frequency band.Too
large C1 will make the start-up slow. See
fig. 10.
2. Set the DC-characteristic that is
required in the PTT specification or in case
of a system telephone,in the PBX
specification (R6).There are also internal
circuit dependent requirements like supply
voltages etc.
3. Set the attac point where the line
length regulation ( if used ) is supposed to
cut in. Note that in some countries the line
length regulation is not allowed. In most
cases the end result is better and more
readily achieved by using the line length
regulation (line loss compensation) than
without.
4. Set the transmitter gain and
frequency response.
5. Set the receiver gain and frequency
response. See text how to limit the max.
swing.
6. Adjust the side tone balancing
network if used.The network in most cases
is just a coarse resistive divider to take
care of the first order of balancing. The fine
balancing is done by the DSP in the sys-
tem.
7. Set the RFI suppression
components in case necessary.
8. Circuit protection. Apart from any
other protection devices used in the de-
sign a good practice is to connect a 15V
1W zener diode across the circuit , from
pin 1 to -Line.
Impedance to the line
The AC- impedance to the line is
set by R3, C1 and C2. Fig.6. The circuits
relatively high parallel impedance will not
influence the line impedance to any
noticeable extent.At low frequencies the
influence of C1 can not be neglected.
Series resistance of C1 that
is dependent on the temperature and the
quality of the component will cause some
of the line signal to enter pin 4. This
generates a closed loop in the transmitter
amplifier that in its turn will create an
active impedance thus lowering the
impedance to the line. The impedance at
high frequencies is set by C2 that also
acts as a RFI suppressor.
In many specifications the
impedance towards the line is specified as
a complex network. See fig. 6. In case a).
the error signal entering pin 4 is set by the
ratio
Rs/R3 (909
), where in case b). the
ratio at high frequencies will be Rs/220
because the 820
resistor is bypassed by
a capacitor. To help up this situation the
complex network capacitor is connected
directly to ground, case c). making the ratio
Rs/220
+820
and thus lessening the
error signal. Conclusion: Connect like in
case c) when complex impedance is
specified.
DC - characteristic
The DC - characteristic that a
telephone set has to fulfill is mainly given
by the network administrator. Following
parameters are useful to know when the
DC behaviour of the telephone is to be set:
The voltage of the feeding system
The line feeding resistance 2 x.......
ohms.
The maximum current from the line at
zero line length.
The min. current at which the telephone
has to work (basic function).
The lowest and highest voltage
permissible across the telephone set.
The highest voltage that the
telephone may have at different line
currents. Normally set by the
network owners specification.The
lowest voltage for the telephone is
normally set by the voltages that are
needed for the different parts of the
telephone to function. For ex. for
transmitter output amplifier, recei-
ver output amplifier, dialler, speech
switching. R6 will set the slope of the
DC-char. and the rest of the level is
set by some constants in the circuit
as shown in the equation below. The
slope of the DC-char. will also
influence the line length regulation
(when used ) and thus the gain of
both transmitter and receiver. See
the table under gain regulation. R6
also acts as power protection for the
circuit, this must be kept in mind
when low values of R6 are conside-
red. See fig. 7.
V
Line
2
+
1.5
R
6
I
line
V
telephoneline
1.5
V
+
V
line
1
2
+Line
R3
R6
PBL 38 582
+
3
C1
C2
-Line
Rs
1
How to connect a
complex network.
Example:
a)
b)
c)
4
220
820
C
220
+820
//C
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