Philips TEA1085T, TEA1085AT, TEA1085A, TEA1085 Datasheet

INTEGRATED CIRCUITS

DATA SHEET

TEA1085; TEA1085A

Listening-in circuit for line-powered telephone sets

Preliminary specification			March 1992
File under Integrated Circuits, IC03A

Philips Semiconductors	Preliminary specification

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

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

ORDERING INFORMATION

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.

EXTENDED TYPE			PACKAGE
NUMBER	PINS	PIN POSITION		MATERIAL	CODE
TEA1085/TEA1085A	24	DIL		plastic	SOT101B(1)
TEA1085T/TEA1085AT	24	SO24		plastic	SOT137A(2)

Notes

1.SOT101-1; 1998 Jun 18.

2.SOT137-1; 1998 Jun 18.

March 1992

2

Philips Semiconductors	Preliminary specification

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

QUICK REFERENCE DATA

SYMBOL	PARAMETER	CONDITIONS	MIN.	TYP.	MAX.	UNIT
ISUP	input current range		4	-	120	mA
VBB	stabilized supply voltage		-	3.6	-	V
ISUP	current consumption	PD = HIGH	-	55	-	mA
Gv	voltage gain loudspeaker amplifier
		SE	-	35	-	dB
		BTL	-	41	-	dB
DGv	maximum gain reduction with logic		-	18	-	dB
	inputs (3 steps)
ISUP	minimum input current
		POUT = 20 mW typ.	-	15	17	mA
		into 50 W SE
		POUT = 40 mW typ.	-	-	32	mA
		into 50 W BTL
tad(RMS)	Larsen limiter attack delay time VDTI		100	-	200	ms
	jumps from 0 to ³ 100 mV (RMS value)
VDTI(RMS)	Larsen limiter threshold level	Larsen mode	-	7	-	mV
Gv	Larsen limiter preamplifier gain setting		30	-	52	dB
	range
Tamb	operating ambient temperature range		-25	-	+75	°C

March 1992

3

_

1992 March

VBB

pagewidth full ndbook,

(1)

circuit in-Listening

Semiconductors Philips

line

(1)

TEA1060

(LN)

SUP

SDC

THL1

THL2 LLC

DCA

DTI

QLA

TEA1060

SREF

(MIC)

4

2

3

14

13

12

16

15

11

setstelephone

VSS

1

9

LAI−

for

VBB

24

SUPPLY

LARSEN

PREAMPLIFIER

line

PD

19

LEVEL

LARSEN

PD

LIMITER

LEVEL LIMITER

VA

18

-

10

LAI+

powered

(1)

4

TEA1060

VBB

(MIC)

VBB

TEA1085

4

GSC1

8

2

TEA1085A

START

GSC2

7

I-STABILIZATION

2

CIRCUIT

2

SIC

17

LOGIC GAIN

CONTROL

(1)

PEAK AND

RECEIVING

21

QLS1

POWER

CURRENT

AMPLIFIER

AMPLIFIER

22

QLS2

LIMITER

MUTE

23

20

5

6

(1)

DLC

MUTE

LSI1

LSI2

MGR032

TEA1085ATEA1085;

specification Preliminary

(1)

(2)

TEA1060 (VEE)

TEA1060 (QR)

(1)

To TEA1060 (SLPE).

(2)

See Fig.16.

Fig.1

Block diagram.

Philips Semiconductors	Preliminary specification

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

	PIN CONFIGURATION
	SYMBOL	PIN	DESCRIPTION
	VSS	1	negative supply
	SUP	2	positive supply
	SDC	3	supply amplifier decoupling
	SREF	4	supply reference input
	LSI1	5	loudspeaker amplifier input 1
					handbook, halfpage
	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	VBB 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
	VBB	24	stabilized supply decoupling

VSS	1			VBB
			24
SUP				DLC
	2		23
SDC	3			QLS2
			22
SREF	4			QLS1
			21
LSI1				MUTE
	5		20
LSI2	6	TEA1085	19	PD
GSC2		TEA1085A		VA
	7		18
	8
GSC1			17	SIC
LAI−	9			DCA
			16
LAI+	10			DTI
			15
QLA	11			THL1
			14
LLC	12			THL2
			13
		MLA415

Fig.2 Pin configuration.

March 1992

5

Philips Semiconductors	Preliminary specification

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

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.

handbook, full pagewidth

VCC	LN						SREF	SUP
	MIC+						LAI+

TEA1060

TEA1085

QLS

MIC−

LAI− TEA1085A

LINE

QR

VEE

LSI1 LSI2 VSS

SLPE

to TEA1060

(SLPE)

MGR033

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

March 1992

6

Philips Semiconductors	Preliminary specification

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

Supply; SUP, SREF, VBB, VSS and VA

The line current is divided into ITR for the TEA1060 and ISUP for the TEA1085/TEA1085A. The supply arrangement is illustrated in Fig.4.

handbook, full pagewidth	Iline			ISUP	SUP	TR1		VBB
	ICC	R1	ITR	R20
					Vint	TR2
								IBBO
		VCC		LN			VOLTAGE
					SREF
							STABILIZER
		TEA1060						C20
LINE						IBIAS
					TEA1085
		VEE		SLPE	TEA1085A		VSS	VA
								R38
								MGR034
				R9
ITR is constant: ITR = Vint / R20; ISUP = Iline − ICC − ITR
					Fig.4 Supply arrangement.

Where:
Vint	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
ICC	is the internal current consumption of the
	TEA106X (≈ 1 mA)

A practical value for R20 is 150 Ω. This value of resistance produces a value for ITR = 2 mA and ISUP = Iline − 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 VSUP 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

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 (VSUP − VSS) is determined by the transmission IC (VLN−SLPE); thus:

VSUP − VSS = VLN−SLPE + Vint.

The minimum DC voltage that can be applied to this input is VBB(max) + 0.4 V.

Where: VBB(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 (ISUP0) is typically 4.2 mA (where VSUP − VSS = 4.5 V, MUTE off). Thus the current available

for powering the loudspeaker is ISUP − ISUP0.

The current ISUP0 consists of a bias current of ≈ 0.4 mA for the circuitry connected to SUP and current IBB0 of ≈ 3.8 mA which is used for the circuitry connected to VBB (see Fig.4).

March 1992

7

Philips Semiconductors	Preliminary specification

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

5.5															MGR035
ndbook, halfpage
VBB
(V)
5.1
4.7
4.3
3.9																				VBB = 3.60 V
3.5
		102													103
10											R38 (kΩ)

Fig.5 Stabilized supply voltage as a function of R38.

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	gain	gain reduction
			(dB)	(dB)
	0	0	35	0
	0	1	28.7	6.3
	1	0	22.2	12.2
	1	1	17	18

Where:

0 = connection to VSS or left open-circuit 1 = applying a voltage ³ VSS + 1.5 V

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 mH 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 W 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

Philips Semiconductors	Preliminary specification

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

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)

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.

∙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; 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 VSS). 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.

handbook, full pagewidth LSI1

MUTE

QLS1

standby

listening-in

standby

MGR036

Fig.6 Mute toggle function of the TEA1085.

handbook, full pagewidth

	VBB
MUTE	MUTE
	10 kΩ
	MLA055
(a) Break contact.	(b) Make contact.

Fig.7 Mute switch alternatives with the TEA1085.

March 1992

9

Philips Semiconductors	Preliminary specification

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

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 IBBO (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 VSUP = 4.5 V in the following equation:

ISUP(PD) = IBIAS(PD) = (VSUP − 2Vd) / Ra

(where 4.2 V < VSUP < 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 VSS. The preferred value is 120 kΩ. The internal reference current is given by the following equation:

ISIC = 1.25 / R36; when R36 = 120 kΩ, ISIC = 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):

Apre = VQLA / 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).

handbook, full pagewidth

VBB

C25

R32

R29

R30

IDCA

R33

C23

R26

DCA

LAI−

−

−

C24

VM

R25

DTI

LAI+

+

QLA

+

C22

VQLA

R27

VBB

R31

LLC

LARSEN

VSS

DETECTOR

R28

THL1

THL2

R35

R34

MGR037

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

March 1992

10