mc34216adwf Freescale Semiconductor, Inc, mc34216adwf Datasheet - Page 14

• Manufacturer Part Number: mc34216adwf
• Description: Programmable Telephone Line Interface Circuit With Loudspeaker Amplifier
• Manufacturer: Freescale Semiconductor, Inc

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.
Handsfree
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
Phone Line
Reduced
Nominal
14
The microphone threshold reduces the gain in the acoustic
A speakerphone application for handsfree conversation
R4
Figure 12. Behavior of the Microphone
Gain
C4
Hookswitch
33 n
Threshold Feature
SAI of
MC34216A
R1
110 n
Figure 13. Concept of Ringing Via Loudspeaker
Application
Off Hook
A
A
R24
TX
LSP
Iu (Arms)
LI
R
Gnd
TCA3385
in
MC34216A
RDO
DRV
V
CO
CC
controller
Micro-
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 anti–distortion
circuitry and line current regulation. More details about this
application can be found in the user manual.
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.
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 V CC to the output current of the ringing
melody generator. No ringing melody is made audible when
V CC is below 3.8 V and the maximum volume is reached
when V CC has reached 5.5 V.
conditions, the current consumption of the MC34216A in
ringing mode is reduced down to 2.0 mA.
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.
T1
D10
C8
The MC34216A offers the possibility to generate a ringing
As can be seen in Figure 13, the high voltage ring signal is
To ensure optimum output power under low line current
The MC34216A offers the possibility to listen to the ringing
L1
Bus
C7
MOTOROLA ANALOG IC DEVICE DATA
V CC
LPI
I
and Melody
R
Generator
Regulator
Ringer
Supply
MC34216A
R30
Gnd
LPO
C24