TEA1068T Philips Semiconductors, TEA1068T Datasheet - Page 5

• Manufacturer Part Number: TEA1068T
• Description: Versatile telephone transmission circuit with dialler interface
• Manufacturer: Philips Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
Supplies: V
Power for the TEA1068 and its peripheral circuits is usually
obtained from the telephone line. The TEA1068 develops
its own supply at V
supply voltage VCC 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
regulator is decoupled by a capacitor between REG and
VEE .
The DC current flowing into the set is determined by the
exchange voltage (Vexch ) , the feeding bridge resistance,
(R
An internal current stabilizer is set by a resistor of 3.6 k
between the current stabilizer pin STAB and V
(see Fig.9).
If the line current I
required by the circuit itself (approximately 1 mA) plus the
current I
V
via LN.
The regulated voltage on the line terminal (VLN ) can be
calculated as:
or
where V
compensated reference voltage of 4.2 V and R9 is an
external resistor connected between SLPE and V
The preferred value for R9 is 20 . Changing the value of
R9 will also affect microphone gain, DTMF gain, gain
control characteristics, side-tone level, the maximum
output swing on LN and the DC characteristics (especially
at lower voltages).
Under normal conditions, when I
the static behaviour of the circuit is that of a 4.2 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 (see Fig.4).
The internal reference voltage can be adjusted by means
of an external resistor (R
between LN and REG, will decrease the internal reference
voltage; when connected between REG and SLPE, it will
increase the internal reference voltage. Current (Ip)
available from V
1996 Apr 23
CC
V
VLN= V
exch
Versatile telephone transmission circuit
with dialler interface
LN
, then the voltage regulator diverts the excess current
) and the DC resistance of the telephone line (R
= V
p
ref
required by the peripheral circuits connected to
ref
ref
is an internally generated temperature
CC
+ I SLPE R9
+ [(Iline I
, LN, SLPE, REG and STAB
CC
line
CC
for supplying peripheral circuits
CC
exceeds the current ICC+ 0.5 mA
and regulates its voltage drop. The
CC
and VEE ; the internal voltage
VA
). This resistor, connected
0.5
SLPE
10
3
)
>> I
Ip]
CC
+ 0.5 mA + Ip,
R9
EE
EE
.
line
).
5
handbook, halfpage
depends on external components and on the line current.
Figure 10 shows this current for V
VCC> 3 V, this being the minimum supply voltage for most
CMOS circuits, including voltage drop for an enable diode.
If MUTE is LOW, the available current is further reduced
when the receiving amplifier is driven.
Microphone inputs MIC+ and MIC and gain
adjustment pins GAS1 and GAS2
The TEA1068 has symmetrical microphone inputs.
Its input impedance is 64 k (2
gain is typically 52 dB (when R7
Dynamic, magnetic, piezoelectric or electret (with built-in
FET source followers) microphones can be used.
The arrangements with the microphone types mentioned
are shown in Fig.11.
The gain of the microphone amplifier can be adjusted
between 44 dB and 60 dB. The gain is proportional to the
value of the external resistor R7 connected between GAS1
and GAS2. An external capacitor C6 of 100 pF between
GAS1 and SLPE is required to ensure stability. A larger
value may be chosen to obtain a first-order low-pass filter.
The cut-off frequency corresponds with the time constant
R7
R
L
eq
p
C6.
17.5 k
C3
V EE
Fig.4 Equivalent impedance circuit.
LN
R9
R
p
R9
20
L eq
V ref
REG
R p
C3
4.7 F
32 k ) and its voltage
CC
MBA454
68 k ; see Fig.14).
Product specification
> 2.2 V and for
V CC
R1
TEA1068
C1
100 F