MC34216A Datasheet, PDF (8/20 Pages) Motorola, Inc – PROGRAMMABLE TELEPHONE LINE INTERFACE CIRCUIT WITH LOUDSPEAKER AMPLIFIER

MC34216A
PIN FUNCTION DESCRIPTION (continued)
Pin
Symbol
Description
21
VCC
Supply Voltage
22
Gnd
Large Signal Ground
23
LPO
Loudspeaker Amplifier Output
24
LPI
Loudspeaker Amplifier Input
25
RXI
Receive Amplifier Input
26
RXO1
Receive Amplifier Output
27
RXO2
Receive Amplifier Output
28
AGC
Loudspeaker AGC Timing
CIRCUIT DESCRIPTION
Concept
With the MC34216A, a microcontroller and a switched
mode power supply, a telephone set with listening–in function
and ringing via loudspeaker can be built as shown in
Figure 1.
In off–hook position, the application is in speech mode. The
line current flows through transistor T2 and supplies the
application at the supply point VCC which is stabilized by the
MC34216A. The Vline, Iline characteristic is programmed by
the microcontroller and adjusted by the external components
Z0, Z1, Z21 and R1 which are in a regulator loop, acting on
transistor T2. The ac impedance is generated in a similar way.
Handset and loudspeaker can be connected directly to the
MC34216A to perform handset and listening–in operation.
Via the bus, the microcontroller programs the MC34216A to
perform the DTMF/pulse–dialing and supervise the device.
The user keyboard has to be connected to the microcontroller.
In on–hook position, the SMPS supplies the application in
presence of a ringing signal. The microcontroller programs
the MC34216A and a ringing melody can be generated via
the loudspeaker.
The block diagram of the MC34216A (see Figure 2),
shows the basic blocks of the device plus the essential
external components.
Hookswitch
Figure 1. Telephone Concept with MC34216A
Z1
Z0
Z21
T2
VCC
A/B
Handset
MC34216A
Micro
Loudspeaker
R1
Gnd
SMPS
8
MOTOROLA ANALOG IC DEVICE DATA