Philips Semiconductors
Product specification
Low voltage versatile telephone
transmission circuit with dialler interface
FUNCTIONAL DESCRIPTION
Supply: V
CC
, LN, SLPE, REG and STAB
Power for the TEA1067 and its peripheral circuits is usually
obtained from the telephone line. The IC develops its own
supply at V
CC
and regulates its voltage drop. The supply
voltage V
CC
may also be used to supply external circuits
e.g. dialling and control circuits.
Decoupling of the supply voltage is performed by a
capacitor between V
CC
and V
EE
while the internal voltage
regulator is decoupled by a capacitor between REG and
V
EE
.
The DC current drawn by the device will vary in
accordance with varying values of the exchange voltage
(V
exch
), the feeding bridge resistance (R
exch
), and the DC
resistance of the telephone line (R
line
).
The TEA1067 has an internal current stabilizer working at
a level determined by a 3.6 kΩ resistor connected
between STAB and V
EE
(see Fig.7). When the line current
(I
line
) is more than 0.5 mA greater than the sum of the IC
supply current (I
CC
) and the current drawn by the
peripheral circuitry connected to V
CC
(I
p
) the excess
current is shunted to V
EE
via LN.
The regulated voltage on the line terminal (V
LN
) can be
calculated as:
V
LN
= V
ref
+
I
SLPE
×
R9; or
V
LN
= V
ref
+
[(I
line
−
I
CC
−
0.5
×
10
−3
A)
−
I
p
]
×
R9
Where V
ref
is an internally generated temperature
compensated reference voltage of 3.6 V and R9 is an
external resistor connected between SLPE and V
EE
.
TEA1067
In normal use the value of R9 would be 20
Ω.
Changing the
value of R9 will also affect microphone gain, DTMF gain,
gain control characteristics, side-tone level and maximum
output swing on LN, and the DC characteristics (especially
at the lower voltages).
Under normal conditions, when I
SLPE
>> I
CC
+
0.5 mA
+
I
p
,
the static behaviour of the circuit is that of a 3.6 V regulator
diode with an internal resistance equal to that of R9. In the
audio frequency range the dynamic impedance is largely
determined by R1. Fig.4 shows the equivalent impedance
of the circuit.
At line currents below 9 mA the internal reference voltage
is automatically adjusted to a lower value (typically 1.6 V
at 1 mA). This means that the operation of more sets in
parallel is possible with DC line voltages (excluding the
polarity guard) down to an absolute minimum voltage of
1.6 V. With line currents below 9 mA the circuit has limited
sending and receiving levels. The internal reference
voltage can be adjusted by means of an external resistor
(R
VA
). This resistor connected between LN and REG will
decrease the internal reference voltage, connected
between REG and SLPE it will increase the internal
reference voltage.
Current (I
p
) available from V
CC
for peripheral circuits
depends on the external components used. Fig.10 shows
this current for V
CC
>
2.2 V. If MUTE is LOW when the
receiving amplifier is driven the available current is further
reduced. Current availability can be increased by
connecting the supply IC (TEA1081) in parallel with R1, as
shown in Fig.17 (c), or by increasing the DC line voltage by
means of an external resistor (R
VA
) connected between
REG and SLPE.
June 1990
5
PHILIPS [ NXP SEMICONDUCTORS ]
