March 1994 6
Philips Semiconductors Product specification
Call progress monitor for line powered
telephone sets
TEA1083; TEA1083A
The circuit stabilizes its own supply voltage at VBB.
Transistor TR1 provides the supplies for the internal
circuits. Transistor TR2 is used to minimize signal
distortion on the line by momentarily diverting the input
current to VSS whenever the instantaneous value of the
voltage at V
SUP
drops below the supply voltage VBB. VBB is
fixed to a typical value of 2.95 V.
The supply at VBB is decoupled with respect to VSS by a
220 µF capacitor (C20).
The DC voltage (V
SUP
− VSS) is determined by the
transmission IC and V
int
; thus
V
SUP
− VSS = V
LN−SLPE
+ V
int
.
The reference voltage of the transmission IC has to be
adjusted to a level where V
SUP
− V
BB (max)
is greater than
400 mV. The minimum voltage space between SUP and
VBB (400 mV) is required to maintain a 'high' efficiency of
the internal supply for mean speech levels. V
BB (max)
is the
specified maximum level.
The internal current consumption of the TEA1083/83A
(I
SUP0
) is typically 2.5 mA (where V
SUP
− VSS= 3.6 V).
The current I
SUP0
consists of currents I
BIAS
(approximately
0.4 mA) for the circuitry connected to SUP and I
BB0
(approximately 2.1 mA) for the internal circuitry connected
to VBB(see Fig.6).
LOUDSPEAKER AMPLIFIER (LSI1/LSI2 and QLS)
The TEA1083/83A has symmetrical inputs at LSI1 and
LSI2. The input signal is normally taken from the earpiece
output of the transmission circuit (see Fig.5) and/or from
the signal output of the DTMF generator via a resistive
attenuator.
The attenuation factor must be chosen in accordance with
the output levels from the transmission IC and/or DTMF
generator and, in accordance with the required output
power and permitted signal distortion from the
loudspeaker signal.
The output QLS drives the loudspeaker as a single-ended
load. The output stage has been optimized for use with a
50 Ω loudspeaker (e.g. Philips type AD2071). The
loudspeaker amplifier is enabled when the LSE input goes
HIGH. The gain of the amplifier is fixed at 35 dB.
Volume control of the loudspeaker signal can be obtained
by using a level control at the input (see Fig.5).
The maximum voltage swing at the QLS output is
V
O(p-p)
= 2.5 V (typical with 50 Ω load). The input level
V
LSI
is approximately 16 mV(rms) and the supply current
I
SUP
> 11 mA. In this condition the signal is limited by the
available voltage space (VBB). Higher input levels and/or
lower supply currents will result in an increase of the
harmonic distortion due to signal clipping.
With a limit of 2.5 V (p-p), the maximum output swing is
dependent on the supply current and loudspeaker
impedance. It can be approximated, for low distortions, by
the following equation:
V
O(p-p)
=2×(I
SUP
− I
SUPO
) ×π×R
LS
Where;
• V
O(p-p)
= the peak-to-peak level of the loudspeaker
• RLS= the loudspeaker impedance
• I
SUPO
= 2.5 mA (typ.)
POWER-DOWN INPUT (PD)
During pulse dialling or register recall (timed loop break)
the telephone line is interrupted, thereby breaking the
supply current to the transmission IC. The capacitor
connected to V
BB
provides the supply for the
TEA1083/83A during the supply breaks.
By making the PD input HIGH during the loop break, the
requirement on the capacitor is eased and, consequently,
the internal current consumption I
BB0
(see Fig.5) is
reduced from 2.1 mA to 400 µA typically. Transistors TR1
and TR2 are inhibited during power-down and the bias
current is reduced from approximately 400 µA to
approximately 50 µA with V
SUP
= 3.6 V in the following
equation:
I
SUP(PD)
= I
BIAS(PD)
= (V
SUP
− 2Vd)/Ra
Where 3.6 < V
SUP
< VBB+ 3V
2Vd is the voltage drop across 2 internal diodes
(approximately 1.3 V)
Ra is an internal resistor (typical 50 kΩ)
LOUDSPEAKER ENABLE INPUT (LSE)
The LSE input has a pull-down structure. It switches the
loudspeaker amplifier, in the monitoring condition, by
applying a HIGH level at the input. The amplifier is in the
standby condition when LSE is LOW (input open-circuit or
connected to V
SS
).