TEA1110AL-S14-R datasheet(8/9 Pages) UTC

8 / 9 page

TEA1110A

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

8 of 9

www.unisonic.com.tw

QW-R108-014.C

FUNCTIONAL DESCRIPTION(Cont.)

Set impedance

The dynamic impedance is mainly determined by the RCC resistor within the audio frequency range. The

equivalent impedance of the circuit is shown in Fig.5.

Rcc

619Ω

Vcc

Cvcc

100μF

REG

CREG

RSLPE

LEQ

Vref

SLPE

VEE

LEQ=CREG × RSLPE × Rp

Rp=internal resistance

Rp=15.5kΩ

Fig.5 Equivalent impedance between LN and VEE

20Ω

4.7μF

Microphone amplifier (pins MIC+ and MIC-)

The UTC TEA1110A has symmetrical microphone inputs. The input impedance between pin MIC+ and pin MIC-

is 64kΩ (2 × 32kΩ). On this microphone amplifier, automatic gain control is used for line loss compensation.

Receiving amplifier (pins IR, GAR and QR)

The receiving amplifier has one input (IR) and one output (QR). The input impedance between pin IR and pin

VEE is 20kΩ. Connecting an external resistor RGAR between pins GAR and QR can decrease the voltage gain within

14dB from pin IR to pin QR. The two external capacitors CGAR (connected between pins GAR and QR) and CGARS

(connected between GAR and VEE) ensure stability, the CGAR capacitor provides a first-order low-pass filter. The

cut-off frequency corresponds to the time constant CGAR × (RGARint // RGAR). And the RGARint is the internal resistor

connected between pins GAR and QR which sets a 125 kW typ gain. The condition CGARS = 10 ×CGAR is required to

ensure stability.

The output voltage of the receiving amplifier is for continuous wave drive specially. The maximum output swing

depends on the DC line voltage, the RCC resistor, the ICC current consumption of the circuit, the IP current

consumption of the peripheral circuits and the load impedance.

On this receiving amplifier automatic gain control is used for line loss compensation.

Automatic gain control (pin AGC)

The UTC TEA1110A performs automatic line loss compensation. The automatic gain control varies both the

gain of the microphone amplifier and receiving amplifier in accordance with the DC line current within 5.9 dB (which

corresponds approximately to a line length of 5 km for a 0.5 mm diameter twisted-pair copper cable with a DC

resistance of 176Ω/km and an average attenuation of 1.2dB/km).

The IC can be used with different configurations of feeding bridge (supply voltage and bridge resistance) by the

means of connecting an external resistor RAGC between pins AGC and VEE. The line currents ISTART and ISTOP can

be increased by this resistor (the ratio between ISTART and ISTOP is not affected by the resistor). When pin AGC is in

the open-circuit condition, the AGC function is inactive.

Mute function (pin MUTE MUTE)

The mute function performs the switching between the speech mode and the dialling mode. When the MUTE

is in a low level, the DTMF input is active and the microphone and receiving amplifiers inputs are inactive. When the

MUTE is in a high level, the microphone and receiving amplifiers inputs are active while the DTMF input is inactive.

The input includes a pull-up resistor.

DTMF amplifier (pin DTMF)

When the DTMF amplifier is inactive, dialling tones that can be heard in the earpiece at a low level may be sent

on line. The UTC TEA1110A has an asymmetrical DTMF input. The input impedance between DTMF and VEE is

20kΩ. The automatic gain control has no effect on the DTMF amplifier.

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