# L3281 Low Voltage Telephone Speech Circuit

## Overview
· Low voltage operation: Down to 1.6V / 6.5mA
· Supports DTMF & Beep Tone inputs
· External muting for both earphone and microphone
· Suitable for dynamic earphones and dynamic/electret microphones
· Includes AGC (Automatic Gain Control) on sending and receiving paths

## Key Features
· Voltage: Operates down to 1.6V with 6.5mA current draw
· Interfaces: Compatible with DTMF and beep tone inputs
· Audio Support: Works with dynamic earphones and both dynamic and electret microphones.
· Gain Control: Automatic Gain Control on both transmitting and receiving sides.
· Impedance: Line impedance: 500-700 ohms. Microphone Input Impedance: 40k ohms
· Muting: External muting control for earphone and microphone.
· Package Options: Available in DIP14 and SO14 packages.

## Electrical Characteristics (Typical Values)
· Line Voltage: 3.4V @ 20mA, 6.0V @ 50mA, 8V @ 80mA
· CMRR: 50 dB
· Sending Gain (Gtx): 31.5 dB @ 20mA
· Receiving Gain (Grx): -10.7 dB @ 20mA
· THD (Total Harmonic Distortion): ≤ 5%
· Zener Voltage (Pin 5): 4.2 - 6.2V @ 1mA

## Functional Description
· Two/Four Wire Conversion: Based on a Wheatstone bridge configuration.
· Muting Logic: Controlled by a dedicated pin (Pin 10) for dial/speak modes.
· DC Regulation: Provides stable DC impedance for biasing.
· AGC: Adjusts gain based on line current for optimal signal quality.

## Package Dimensions
· DIP14: Details provided for dimensions (mm and inches).
· SO14: Details provided for dimensions (mm and inches).

## Important Notes
· This is preliminary data subject to change.
· Not authorized for use in life support devices without express written approval.
· Specifications are subject to change without notice.