tea1118t NXP Semiconductors, tea1118t Datasheet - Page 7

• Manufacturer Part Number: tea1118t
• Description: Versatile Cordless Transmisssion Circuit
• Manufacturer: NXP Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
All data given in this chapter are typical values, except
when otherwise specified.
Supplies (pins LN, SLPE, V
The supply for the TEA1118 and TEA1118A and their
peripherals is obtained from the telephone line.
The ICs generate a stabilized reference voltage (V
between pins LN and SLPE. This reference voltage is
equal to 3.35 V, is temperature compensated and can be
adjusted by means of an external resistor (R
increased by connecting the R
pins REG and SLPE (see Fig.11), or decreased by
connecting the R
The voltage at pin REG is used by the internal regulator to
generate the stabilized reference voltage and is decoupled
by a capacitor (C
This capacitor, converted into an equivalent inductance
(see Section “Set impedance”), realizes the set impedance
conversion from its DC value (R
(R
SLPE is proportional to the line current. Figure 7 illustrates
the supply configuration.
The ICs regulate the line voltage at pin LN, and it can be
calculated as follows:
V
I
where:
The preferred value for R
affect more than the DC characteristics; it also influences
the transmit gain and the DTMF gain (TEA1118A only), the
gain control characteristics, the sidetone level and the
maximum output swing on the line.
The internal circuitry of the TEA1118 and TEA1118A is
supplied from pin V
the line voltage by means of a resistor (R
decoupled by a capacitor C
supply peripheral circuits such as dialling or control
circuits. The V
consumed by the IC and the peripheral circuits as shown
1997 Jul 14
SLPE
LN
I
I
I
I*: current consumed between LN and V
I
via LN.
CC
Versatile cordless transmisssion circuit
line
CC
P
sh
: supply current for peripheral circuits
= V
: the excess line current shunted to SLPE (and V
: current consumption of the IC
in the audio-frequency range). The voltage at pin
: line current
= I
ref
line
+ R
I
SLPE
CC
CC
VA
REG
voltage depends on the current
I
CC
P
resistor between pins REG and LN.
) which is connected to V
I
SLPE
. This voltage supply is derived from
I* = I
SLPE
VCC
sh
CC
is 20 . Changing R
VA
. It may also be used to
SLPE
and REG)
resistor between
) to its AC value
CC
EE
) and must be
VA
EE
). It can be
.
SLPE
ref
)
EE
will
)
7
by the formula (see also Figs 8 and 9). R
internal equivalent resistance of the voltage supply point,
and I
earpiece amplifier.
V
V
The DC line current flowing into the set is determined by
the exchange supply voltage (V
resistance (R
(R
below 7.5 mA, the internal reference voltage (generating
V
This means that more sets can operate in parallel with DC
line voltages (excluding the polarity guard) down to an
absolute minimum voltage of 1.6 V. At currents below
7.5 mA, the circuit has limited transmit and receive levels.
This is called the low voltage area.
Set impedance
In the audio frequency range, the dynamic impedance is
mainly determined by the R
impedance of the circuits is illustrated in Fig.10.
Transmit amplifier (pins TX+, TX and GAT)
The TEA1118 and TEA1118A have symmetrical transmit
inputs. The input impedance between pins TX+ and TX is
equal to 62.5 k ; the input impedance between pins
TX+/TX and V
pins TX+/TX to pin LN is set at 11.3 dB.
Automatic gain control is provided on this amplifier for line
loss compensation.
The gain of the TEA1118 can be decreased by connecting
an external resistor R
The adjustment range is equal to 6 dB. A capacitor C
connected between pins GAT and REG can be used to
provide a first-order low-pass filter. The cut-off frequency
corresponds to the time constant C
R
typical value of 27 k .
Transmit mute (pin TMUTE; TEA1118A only)
The transmit amplifier can be disabled by activating the
transmit mute function. When TMUTE is LOW, the normal
speech mode is entered, depending on the level on MUTE.
When TMUTE is HIGH, the transmit amplifier inputs are
disabled while the DTMF input is enabled (no confidence
tone is provided). The voltage gain between LN and
TX+/TX is attenuated; the gain reduction is 80 dB.
CC
CC0
ref
GATint
line
) is automatically adjusted to a lower value.
= V
rec
) and the reference voltage (V
= V
is the internal resistor which sets the gain with a
is the current consumed by the output stage of the
CC0
LN
exch
R
R
CC
EE
CCint
), the DC resistance of the telephone line
is equal 36.5 k
I
CC
GAT
(I
TEA1118; TEA1118A
P
between pins GAT and REG.
I
CC
rec
)
resistor. The equivalent
exch
GAT
ref
), the feeding bridge
The voltage gain from
Product specification
). With line currents
CCint
R
GATint
is the
// R
GAT
GAT
).