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TEA1085

Listening-in circuit for line-powered telephone sets

Philips Electronics 

Philips Semiconductors

Listening-in circuit for line-powered

telephone sets

Preliminary specification

TEA1085; TEA1085A

ndbook5, .h5alfpage

VBB

(V)

5.1

4.7

4.3

3.9

3.5

10

MGR035

Logic gain control (GSC1 and GSC2) pins 7 and 8

The logic inputs GSC1 and GSC2 can be used to reduce

the gain of the loudspeaker amplifier by means of the logic

gain control function in 3 steps of 6 dB.

Table 1 Data for microcontroller drive of logic inputs

GSC2 GSC1

0

0

0

1

1

0

1

1

gain

(dB)

35

28.7

22.2

17

gain reduction

(dB)

0

6.3

12.2

18

VBB = 3.60 V Where:

102

R38 (kΩ)

103

0 = connection to VSS or left open-circuit

1 = applying a voltage ≥ VSS + 1.5 V

Fig.5 Stabilized supply voltage as a function of

R38.

Supply amplifier stability (SDC) pin 3

To ensure stability of the TEA1085/TEA1085A, in

combination with a transmission IC of the TEA1060 family,

a 47 pF capacitor connected between SDC and SUP and

a 150 µH coil connected between SUP and the positive

line terminal (Fig.16) is required.

Loudspeaker amplifier (LSI1/LSI2 and QLS1/QLS2)

pins 5/6, 21/22

The TEA1085/TEA1085A have symmetrical inputs at LSI1

and LSI2. The input signal is normally taken from the

earpiece output of the transmission circuit via a resistive

attenuator (see Fig.3). The amount of attenuation must be

chosen in accordance with the receive gain of the

transmission IC (which depends on the sensitivity of the

earpiece transducer). The maximum input signal level is

450 mV(RMS) at Tamb = +25 °C.

The outputs QLS1 and QLS2 can be used for single ended

drive (SE) or bridge tied load drive (BTL). The output

stages have been optimized for use with a 50 Ω

loudspeaker (e.g. Philips type AD2071).

The gain of the amplifier is fixed to ≈ 35 dB for the SE drive

and ≈ 41 dB for the BTL drive (when the inputs for logic

control are left open-circuit or are connected to VSS).

The volume control can be obtained by using a

potentiometer at the input and/or by the logic control

function.

March 1992

8

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