|TEA1110A||Low voltage versatile telephone transmission circuit with dialler interface|
|TEA1110A Datasheet PDF : 20 Pages |
Low voltage versatile telephone
transmission circuit with dialler interface
handbook, full pagewidth
from pre amp
Fig.3 Supply configuration.
100 µF circuits
The internal circuitry of the TEA1110A is supplied from
pin VCC. This voltage supply is derived from the line
voltage by means of a resistor (RCC) and must be
decoupled by a capacitor CVCC. It may also be used to
supply peripheral circuits such as dialling or control
circuits. The VCC voltage depends on the current
consumed by the IC and the peripheral circuits as shown
by the formula:
VCC = VCC0 – RCCint × (IP – Irec)
VCC0 = VLN – RCC × ICC (see also Figs 5 and 6).
RCCint is the internal equivalent resistance of the voltage
supply, and Irec is the current consumed by the output
stage of the earpiece amplifier.
The DC line current flowing into the set is determined by
the exchange supply voltage (Vexch), the feeding bridge
resistance (Rexch), the DC resistance of the telephone line
(Rline) and the reference voltage (Vref). With line currents
below 7.5 mA, the internal reference voltage (generating
Vref) is automatically adjusted to a lower value. 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 sending and receiving levels. This is
called the low voltage area.
(1) Influence of RVA on Vref.
(2) Vref without influence of RVA.
Fig.4 Reference voltage adjustment by RVA.
1997 Apr 22
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