MC34216A Datasheet, PDF(14/20 Page) Motorola, Inc – PROGRAMMABLE TELEPHONE LINE INTERFACE CIRCUIT WITH LOUDSPEAKER AMPLIFIER

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MC34216A Datasheet, PDF (14/20 Pages) Motorola, Inc – PROGRAMMABLE TELEPHONE LINE INTERFACE CIRCUIT WITH LOUDSPEAKER AMPLIFIER

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MC34216A

The microphone threshold reduces the gain in the acoustic

feedback loop by 7.0 dB. When there is no, or only a small

microphone signal, the gain in the transmit path is reduced by

7.0 dB with respect to nominal. The loudspeaker gain is then

at its nominal value. At a high microphone input current, the

microphone gain is back to its nominal value and the

loudspeaker gain reduced by 7.0 dB. The behavior of the

microphone threshold feature is depicted in Figure 12.

Figure 12. Behavior of the Microphone

Threshold Feature

Gain

Nominal

A TX

Reduced

A LSP

Iu (Arms)

33 n

110 n

Handsfree

A speakerphone application for handsfree conversation

can easily be made with the MC34216A by adding one of

the Motorola speakerphone cores to it. The TXI input can be

used to amplify the transmit signal and the earphone output

can be used to monitor the receive signal. The receive

output of the speakerphone core can be connected to

AHO1. When programming the MC34216A in speakerphone

mode, the signal on this pin will be amplified to the

loudspeaker output. In this way, the features and

functionality of the MC34216A are optimally used, like its

powerful supply, loudspeaker amplifier with antiâdistortion

circuitry and line current regulation. More details about this

application can be found in the user manual.

Ringing

The MC34216A offers the possibility to generate a ringing

melody via the loudspeaker, which avoids the use of a piezo

buzzer. The power needed to supply the loudspeaker is

transformed out of the ringer signal by a switched mode

power supply TCA3385. The melody is generated by the

MC34216A and programmed via the microcontroller. This

concept is depicted in Figure 13.

As can be seen in Figure 13, the high voltage ring signal is

first transformed into a low voltage supply point with high

current capability. This is needed because, compared to a

piezo resonator, a loudspeaker is low ohmic. In the ringing

mode, the voltage of the supply point is stabilized by the

MC34216A to 5.5 V. The ringing melody can be programmed

via the microcontroller and is generated internally. The output

signal level is regulated via a gain control loop. The loop

couples the value of VCC to the output current of the ringing

melody generator. No ringing melody is made audible when

VCC is below 3.8 V and the maximum volume is reached

when VCC has reached 5.5 V.

To ensure optimum output power under low line current

conditions, the current consumption of the MC34216A in

ringing mode is reduced down to 2.0 mA.

The MC34216A offers the possibility to listen to the ringing

melody while in the speech mode. Although the feeding

conditions are not equal for ringing and speech mode, this

offers the user the possibility to program his own melody and

to adjust the volume.

Hookswitch

R4 C4

Phone Line

Figure 13. Concept of Ringing Via Loudspeaker

LI CO

R24

DRV

Off Hook

Application

TCA3385

Rin

SAI of

MC34216A

Gnd VCC

RDO

D10

Micro-

controller

VCC Ringer

Gnd

Supply

Regulator

and Melody

Generator

MC34216A

LPO

C24

LPI

R30

Bus

MOTOROLA ANALOG IC DEVICE DATA

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