Philips TEA1085T-C1, TEA1085AT-C1, TEA1085A-C1, TEA1085-C1 Datasheet

DATA SH EET

Preliminary speciﬁcation File under Integrated Circuits, IC03A

March 1992

INTEGRATED CIRCUITS

TEA1085; TEA1085A

Listening-in circuit for line-powered telephone sets

March 1992 2

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

TEA1085; TEA1085A

FEATURES

• Internal supply optimum current split-up

- low constant current (adjustable) in transmission IC

- nearly all line current available for listening-in adjustable supply voltage

• Loudspeaker amplifier dynamic limiter providing low distortion and the

highest possible output power SE or BTL drive for loudspeaker volume control by potentiometer and/or logic inputs (e.g. microcontroller drive) fixed gain of 35 dB

• Larsen level limiter low sensitivity for own speech due to 3rd-order filter

and attack delay adjustable voltage thresholds

• Power down input

• MUTE input

TEA1085/TEA1085A

- clickfree switching between listening-in mode and standby mode

TEA1085

- toggle function

- start-up in standby condition TEA1085A

- logic level input

GENERAL DESCRIPTION

The TEA1085 and TEA1085A are bipolar ICs which have been designed for use in line-powered telephone sets and provide a listening-in facility for the received line signal via a loudspeaker. Nearly all the line current can be used for powering the loudspeaker. The circuits incorporate a supply circuit, loudspeaker amplifier dynamic limiter, MUTE circuit, power-down facility and logic inputs for gain setting. The devices also incorporate a Larsen Level Limiter to reduce howling effects. The ICs are intended for use in conjunction with a transmission circuit of the TEA1060 family.

ORDERING INFORMATION

Notes

1. SOT101-1; 1998 Jun 18.

2. SOT137-1; 1998 Jun 18.

EXTENDED TYPE

NUMBER

PACKAGE

PINS PIN POSITION MATERIAL CODE

TEA1085/TEA1085A 24 DIL plastic SOT101B

(1)

TEA1085T/TEA1085AT 24 SO24 plastic SOT137A

(2)

March 1992 3

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

TEA1085; TEA1085A

QUICK REFERENCE DATA

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

SUP

input current range 4 − 120 mA

stabilized supply voltage − 3.6 − V

SUP

current consumption PD = HIGH − 55 −µA

voltage gain loudspeaker ampliﬁer

SE − 35 − dB BTL − 41 − dB

∆G

maximum gain reduction with logic inputs (3 steps)

− 18 − dB

SUP

minimum input current

OUT

= 20 mW typ.

into 50 Ω SE

− 15 17 mA

OUT

= 40 mW typ.

into 50 Ω BTL

−−32 mA

ad(RMS)

Larsen limiter attack delay time V

DTI

jumps from 0 to ≥ 100 mV (RMS value)

100 − 200 ms

DTI(RMS)

Larsen limiter threshold level Larsen mode − 7 − mV

Larsen limiter preampliﬁer gain setting range

30 − 52 dB

amb

operating ambient temperature range −25 −+75 °C

March 1992 4

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered

telephone sets

TEA1085; TEA1085A

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MGR032

RECEIVING AMPLIFIER

MUTE

PEAK AND CURRENT

LIMITER

POWER

AMPLIFIER

START

CIRCUIT

I-STABILIZATION

LOGIC GAIN

CONTROL

LARSEN

LEVEL

LIMITER

SUPPLY

PREAMPLIFIER

LARSEN

LEVEL LIMITER

MUTE LSI1 LSI2

20 5

DLC

SUP3SDC

SREF

QLA 11

DTI 15

TEA1060 (VEE) TEA1060 (QR)

TEA1060

(MIC)

TEA1060

(MIC)

(2)

(1)

2221QLS2

QLS1

109LAI+

GSC1 8 GSC2 7

SIC 17

(1)

LAI−

line

TEA1060

(LN)

THL212LLC

THL1

DCA

(1)

TEA1085

TEA1085A

Fig.1 Block diagram.

(1) To TEA1060 (SLPE). (2) See Fig.16.

March 1992 5

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

TEA1085; TEA1085A

PIN CONFIGURATION

SYMBOL PIN DESCRIPTION

1 negative supply SUP 2 positive supply SDC 3 supply ampliﬁer decoupling SREF 4 supply reference input LSI1 5 loudspeaker ampliﬁer input 1 LSI2 6 loudspeaker ampliﬁer input 2 GSC2 7 logic input 2 for gain select GSC1 8 logic input 1 for gain select LAI− 9 Larsen limiter preampliﬁer inverting

input

LAI+ 10 Larsen limiter preampliﬁer

non-inverting input QLA 11 Larsen limiter preampliﬁer output LLC 12 Larsen limiter capacitor THL2 13 Larsen limiter residual threshold level THL1 14 Larsen limiter attack delay threshold

level DTI 15 Larsen limiter detector input DCA 16 Larsen limiter detector current

adjustment SIC 17 Larsen limiter current stabilizer VA 18 V

voltage adjustment PD 19 power-down input MUTE 20 MUTE input QLS1 21 loudspeaker ampliﬁer output 1 QLS2 22 loudspeaker ampliﬁer output 2 DLC 23 dynamic limiter capacitor V

24 stabilized supply decoupling

Fig.2 Pin configuration.

handbook, halfpage

SUP

SDC

SREF

LSI1

LSI2 GSC2 GSC1

LAI−

LAI+

QLA

LLC

DLC QLS2 QLS1

PD VA

MUTE

SIC DCA DTI THL1 THL2

1 2 3 4 5 6 7 8

9 10 11 12

24 23 22 21

20 19 18 17 16 15 14 13

TEA1085

TEA1085A

MLA415

March 1992 6

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

TEA1085; TEA1085A

FUNCTIONAL DESCRIPTION

Figure 1 illustrates a block diagram of the TEA1085/TEA1085A with external components and connections to the transmission IC. The TEA1085/TEA1085A are bipolar ICs which have been designed for use in line-powered telephone sets and provide a listening-in facility for the received line signal via a loudspeaker. Nearly all the line current can be used for powering the loudspeaker. The loudspeaker amplifier consists of a preamplifier, to amplify the earpiece signal from the transmission circuit and, a double push-pull output stage to drive the loudspeaker in the BTL (bridge tied load) or SE (single ended) configuration. The gain of the preamplifier is controlled by a dynamic limiter which prevents high distortion of the loudspeaker signal. This is achieved by preventing clipping of the loudspeaker signal, with respect to the supply voltage, and at too low supply current. Two logic inputs can be used to reduce the gain in 3 steps. Because of acoustic feedback from the loudspeaker to the microphone, howling signals (Larsen effect) can occur on the telephone line and in the loudspeaker. When the Larsen signal exceeds a voltage and time duration threshold the Larsen level limiter (LLL) will reduce the

Larsen signal to a low level within a short period of time by reducing the gain of the receiving preamplifier. This is achieved by using the microphone signal as an input signal which is processed in the LLL via a preamplifier and 3rd-order filter. The MUTE input can be used to enable or disable the loudspeaker amplifier. The MUTE function of the TEA1085 has a toggle input to permit the use of a simple push-button switch. The MUTE function of the TEA1085A has a logic input to operate with a microcontroller. By activating the power-down input the current consumption of the circuit will be reduced, this enables pulse dialling or flash (register recall). An internal start circuit ensures normal start-up of the transmission IC and start-up of the listening-in IC in the standby mode. The TEA1085/TEA1085A are intended for use in conjunction with a member of the TEA1060 family and should be connected between LINE and SLPE of the transmission IC. The transmission characteristics (impedance, gain settings, for example) are not affected. The interconnection between the two ICs is illustrated in Fig.3.

Fig.3 Interconnection of the TEA1085/TEA1085A with the TEA1060.

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MGR033

TEA1060

EE SLPE

MIC+

MIC−

LAI+

LAI−

TEA1085

TEA1085A

SREF SUP

LSI1 LSI2

QLS

LINE

to TEA1060

(SLPE)

March 1992 7

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

TEA1085; TEA1085A

Supply; SUP, SREF, VBB, VSSand VA

The line current is divided into I

for the TEA1060 and I

SUP

for the TEA1085/TEA1085A.

The supply arrangement is illustrated in Fig.4.

Fig.4 Supply arrangement.

handbook, full pagewidth

MGR034

TEA1060

EE SLPE

TEA1085

TEA1085A

line

SUP

C20

SUP

BBO

BIAS

R38

R20

VOLTAGE

STABILIZER

TR1

TR2

SREF

int

LINE

ITR is constant: ITR=V

int

/ R20; I

SUP=Iline

− ICC− I

Where:

A practical value for R20 is 150 Ω. This value of resistance produces a value for I

= 2 mA and I

SUP

= I

line

− 3 mA.

The TEA1085/TEA1085A stabilizes its own supply voltage at VBB. Transistor TR1 provides the supplies for the internal circuits. TR2 is used to minimize the signal distortion on the line by momentarily diverting the input current to VSS whenever the instantaneous value of the voltage V

SUP

drops below the supply voltage VBB. VBB is fixed to a typical value of 3.6 V but can be increased by means of an external resistor (R38) connected between

int

is an internal temperature compensated reference voltage with a typical value of

315 mV between SUP and SREF R20 is a resistor between SUP and SREF I

is the internal current consumption of the

TEA106X (≈ 1 mA)

VA and VSS or decreased by connecting this resistor between VA and VBB. The minimum level on VBB is restricted to 3.0 V; the level of the VBB limiter is also affected (see application report for further information). The supply at VBB is decoupled by a 470 µF capacitor.

The DC voltage (V

SUP

− VSS) is determined by the

transmission IC (V

LN−SLPE

); thus:

SUP

− VSS = V

LN−SLPE

+ V

int

. The minimum DC voltage that can be applied to this input is V

BB(max)

+ 0.4 V.

Where: V

BB(max)

is the worst case supply voltage (this depends on the setting of R38, which is connected between VA and VSS).

The internal current consumption of the TEA1085/TEA1085A (I

SUP0

) is typically 4.2 mA (where

SUP

− VSS = 4.5 V, MUTE off). Thus the current available

for powering the loudspeaker is I

SUP

− I

SUP0

The current I

SUP0

consists of a bias current of ≈ 0.4 mA for

the circuitry connected to SUP and current I

BB0

of≈ 3.8 mA

which is used for the circuitry connected to VBB(see Fig.4).

March 1992 8

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

TEA1085; TEA1085A

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 T

amb

= +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.

Fig.5 Stabilized supply voltage as a function of

R38.

dbook, halfpage

5.5

3.5

MGR035

10 10

3.9

4.3

4.7

5.1

R38 (kΩ)

(V)

VBB = 3.60 V

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

Where:

0 = connection to VSS or left open-circuit 1 = applying a voltage ≥ VSS+ 1.5 V

GSC2 GSC1

gain

(dB)

gain reduction

(dB)

0 0 35 0 0 1 28.7 6.3 1 0 22.2 12.2 1 1 17 18

March 1992 9

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

TEA1085; TEA1085A

Dynamic limiter (DLC) pin 23

To prevent distortion of the signal at the loudspeaker outputs the gain of the amplifier is reduced rapidly when:

• the peaks of the signal at the loudspeaker outputs

exceed an internally determined threshold (voltage limiter)

• the DC current into SUP is insufficient (current limiter)

• the voltage at VBB decreases below an internally

determined threshold, typically 2.9 V (VBB limiter)

The time in which the gain reduction is effected is the 'attack time'; this is very short in the first and third instance and relatively long in the second instance. The circuit will remain in the gain-reduced condition until the peaks of the output signal remain below the threshold level. The gain will then return to a nominal level after a time determined by the capacitor connected to DLC (release time).

MUTE input (MUTE) pin 20; TEA1085A

This MUTE is provided with a logic input to operate with a microcontroller for instance. The loudspeaker amplifier is disabled when the MUTE input is LOW (connected to VSS or open input). A HIGH level at the MUTE input enables the amplifier in the listening-in mode.

MUTE input (MUTE) pin 20; TEA1085

The MUTE function is provided with a toggle input and is designed to switch between the standby condition and the listening-in condition on the rising edge of the input MUTE signal (see Fig.6). In the basic application the MUTE input must be LOW (connected to V

). A simple push-button can be used to operate the MUTE toggle (see Fig.7). Debouncing can be realized by means of a small capacitor connected between MUTE and VSS. An internal start circuit ensures that the circuit always starts up in the standby condition.

Fig.6 Mute toggle function of the TEA1085.

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MGR036

LSI1

QLS1

MUTE

standby standbylistening-in

Fig.7 Mute switch alternatives with the TEA1085.

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MLA055

MUTE MUTE

10 kΩ

(a) Break contact. (b) Make contact.

March 1992 10

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

TEA1085; TEA1085A

Power down input (PD) pin 19

During pulse dialling or register recall (timed loop break) the telephone line is interrupted, thereby breaking the supply to the transmission and listening-in circuits. The capacitor connected to VBB provides the supply for the listening-in circuit 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 (standby) current consumption I

BBO

(Fig.4) at VBB is reduced from 3.8 mA to 400 µA typical. So that the transmission circuit is not affected transistors TR1 and TR2 are inhibited and the bias current is reduced from ≈ 0.4 mA to ≈ 55 µA with V

SUP

= 4.5 V in the following

equation: I

SUP(PD)

= I

BIAS(PD)

= (V

SUP

− 2Vd) / Ra

(where 4.2 V < V

SUP

< VBB+ 3 V)

2Vd = the voltage drop across 2 internal diodes (≈ 1.3 V) Ra = an internal resistor of typical 60 kΩ

Larsen limiter current stabilizer (SIC) pin 17

A current reference is set by resistor R36 between SIC and V

. The preferred value is 120 kΩ. The internal reference

current is given by the following equation:

SIC

= 1.25 / R36; when R36 = 120 kΩ, I

SIC

= 10.5 µA

Changing the value of R36 will affect the timing of the Larsen level limiter system.

Larsen limiter preampliﬁer (LAI1/LAI2 and QLA) pins 9/10 and 11

This circuit amplifies the microphone signal to a level suitable for the Larsen limiter detector. The gain is set by external components (see Fig.8). Normally the gain is set to the same level as the microphone amplifier of the transmission circuit, this ensures that the output signal level at output QLA is equal to the line signal level.

The gain between QLA and the microphone input is given by the following equation (the high-pass filter is not taken into account):

pre

= V

QLA

/ VM = R29 / R26; in the basic application

R25 = R26 = 10 kΩ The gain can be adjusted between 30 dB (R29 = 316 kΩ)

and 52 dB (R29 = 4 MΩ). The impedance result of R28 and R27 in parallel must be equal to R29 (e.g. R27 = R28 = 2 × R29).

Fig.8 Larsen limiter preamplifier and voltage/current converter.

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MGR037

LAI+

LAI−

−

R25

R26

R29

C22

C23

DTI

DCA

THL1 THL2

R27

QLA

C24

R30

R33

R32C25

R31

R35 R34

QLA

R28

LARSEN

DETECTOR

LLC

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