Philips Semiconductors
Product specification
Low voltage transmission circuits with
dialler interface
FUNCTIONAL DESCRIPTION
Supplies V
CC
, LN, SLPE, REG and STAB
Power for the IC and its peripheral circuits is usually
obtained from the telephone line. The supply voltage is
derived from the line via a dropping resistor and regulated
by the IC. 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
. The internal voltage
regulator is decoupled by a capacitor between REG and
V
EE
.
The DC current flowing into the set is determined by the
exchange supply voltage V
exch
, the feeding bridge
resistance R
exch
and the DC resistance of the telephone
line R
line
.
The circuit has an internal current stabilizer operating at a
level determined by a 3.6 kΩ resistor connected between
STAB and V
EE
(see Fig.9). 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
V
LN
= V
ref
+ {(I
line
−
I
CC
−
0.5
×
10
−3
A)
−
I
p
}
×
R9
V
ref
is an internally generated temperature compensated
reference voltage of 3.7 V and R9 is an external resistor
connected between SLPE and V
EE
.
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, sidetone level,
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 3.7 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.3 shows the equivalent impedance
of the circuit.
handbook, halfpage
TEA1062; TEA1062A
LN
L eq
Rp
R1
V ref
R9
20
Ω
V
EE
REG
VCC
C3
4.7
µF
C1
100
µF
MBA454
L
eq
= C3
×
R9
×
R
p
.
R
p
= 16.2 kΩ.
Fig.3 Equivalent impedance 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 more sets can be operated in
parallel with DC line voltages (excluding the polarity guard)
down to an absolute minimum voltage of 1.6 V. At 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 when connected between LN and REG will
decrease the internal reference voltage and when
connected between REG and SLPE 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 (TEA1062) or
MUTE is HIGH (TEA1062A) 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.19 and
Fig.20, or by increasing the DC line voltage by means of
an external resistor (R
VA
) connected between REG and
SLPE (Fig.18).
1997 Sep 03
5
PHILIPS [ NXP SEMICONDUCTORS ]
