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TEA1112 View Datasheet(PDF) - Philips Electronics

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TEA1112 Datasheet PDF : 20 Pages
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Philips Semiconductors
Low voltage versatile telephone
transmission circuits with dialler interface
Product specification
TEA1112; TEA1112A
6.0
handbook, halfpage
Vref
(V)
5.0
MGD176
4.0
3.0
104
(1)
(2)
105
106
107
RVA ()
(1) Influence of RVA on Vref.
(2) Vref without influence of RVA.
Fig.5 Reference voltage adjustment by RVA.
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.
Set impedance
In the audio frequency range, the dynamic impedance is
mainly determined by the RCC resistor. The equivalent
impedance of the circuits is illustrated in Fig.8.
LED supply (pin ILED)
The TEA1112; TEA1112A give an on-hook/off-hook status
indication. This is achieved by a current made available to
drive an LED connected between pins ILED and LN. In the
low voltage area, which corresponds to low line current
conditions, no current is available for this LED.
For line currents higher than a threshold, ILEDstart, the ILED
current increases proportionally to the line current (with a
ratio of one third). The ILED current is internally limited to
19.5 mA (see Fig.9). If no LED device is used in the
application, the ILED pin should be shorted to pin SLPE.
For 17 mA < Iline < 77 mA: ILED = I--l--i-n---e--3------1----7--
This LED driver is referenced to SLPE. Consequently, all
the ILED supply current will flow through the RSLPE resistor.
The AGC characteristics are not disturbed (see Fig.4).
Microphone amplifier (pins MIC+, MICand GAS)
The TEA1112; TEA1112A have symmetrical microphone
inputs. The input impedance between pins MIC+ and
MICis 64 k(2 × 32 k). The voltage gain from
pins MIC+/MICto pin LN is set at 51.8 dB (typ). The gain
can be decreased by connecting an external resistor RGAS
between pins GAS and REG. The adjustment range is
13 dB. A capacitor CGAS connected between pins GAS
and REG can be used to provide a first-order low-pass
filter. The cut-off frequency corresponds to the time
constant CGAS × (RGASint // RGAS). RGASint is the internal
resistor which sets the gain with a typical value of 69 k.
Automatic gain control is provided on this amplifier for line
loss compensation.
Microphone mute (pin MMUTE; TEA1112)
The microphone amplifier can be disabled by activating
the microphone mute function. When MMUTE is LOW, the
normal speech mode is entered, depending on the level on
MUTE (see Table 1). When MMUTE is HIGH, the
microphone amplifier inputs are disabled while the DTMF
input is enabled (no confidence tone is provided).
The voltage gain between LN and MIC+/MICis
attenuated; the gain reduction is 80 dB (typ).
Microphone mute (pin MMUTE; TEA1112A)
The microphone amplifier can be disabled by activating
the microphone mute function. When MMUTE is LOW, the
microphone amplifier inputs are disabled while the DTMF
input is enabled (no confidence tone is provided).
The voltage gain between LN and MIC+/MICis
attenuated; the gain reduction is 80 dB (typ). When
MMUTE is HIGH, the normal speech mode is entered,
depending on the level on MUTE (see Table 1).
1997 Mar 26
6
 

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