Programmable Telephone Line Interface Circuit with Loudspeaker Amplifier

The MC34216 is developed for use in telephone applications where besides the standard telephone functions also the group listening–in feature is required. In cooperation with a microcontroller, the circuit performs all basic telephone functions including DTMF generation and pulse dialing. The listening–in part includes a loudspeaker amplifier, an anti–howling circuit and a strong supply. In combination with the TCA3385, the ringing is performed via the loudspeaker.

FEATURES
Line Driver and Supply
• DC and AC Termination of the Line
• Selectable Masks: France, U.K., Low Voltage
• Current Protection
• Adjustable Set Impedance for Resistive and Complex Termination
• Efficient Supply Point for Loudspeaker Amplifier and Peripherals

Handset Operation
• Transmit and Receive Amplifiers
• Adjustable Sidetone Network
• Line Length AGC
• Microphone and Earpiece Mute
• Earpiece Gain Increase Switch
• Microphone Squelch Function
• Transmit Amplifier Soft Clipping

Dialing and Ringing
• Generates DTMF, Pilot Tones and Ring Signal
• Interrupter Driver for Pulse–Dialing
• Low Current While Pulse–Dialing
• Optimized for Ringing via Loudspeaker
• Programmable Ring Melodies
• Uses Inexpensive 500 kHz Resonator

Loudspeaking Facility
• Integrated Loudspeaker Amplifier
• Peak–to–Peak Limiter Prevents Distortion
• Programmable Volume
• Anti–Howling Circuitry for Group Listening–In
• Interfacing for Handsfree Conversation

Application Areas
• Corded Telephony with Group Listening–In
• Cordless Telephony Base Station with Group Listening–In
• Telephones with Answering Machines
• Fax, Intercom, Modem