Features

• This product is pending obsolescence - contact Linear Technology for more information
• Allows Dynamic Control of Output Frequency,
  Cadence, Amplitude and DC Offset
• Active Tracking Supply Configuration Allows Linear
  Generation of Ring Tone Signal
• No High Voltage Post-Filtering Required
• Capacitive Isolation Eliminates Optocouplers
• Low Distortion Output Meets International
  PTT Requirements
• Differential Input Signal for Noise Immunity
• User Adjustable Active Output Current Limit
• Powered Directly From High Voltage Ringer
  Supply - No Additional Supplies Necessary
• Supply Current: <1mA
• 2% Signal Amplitude Reference
• Available in 14-Pin SO and DIP Packages

Typical Application

Description

The LT1684 is a telecommunication ring tone generator. The IC takes a user-generated pulse width modulated (PWM) input and converts it to a high voltage sine wave suitable for telephone ringing applications.The LT1684 receives capacitor-isolated differential PWM input signals encoded with desired ring output cadence, frequency, and amplitude information. The LT1684 normalizes the pulse amplitude to +/-1.25V for an accurate signal voltage reference. The cadence, frequency and amplitude information is extracted using a multiple-pole active filter/amplifier, producing the output ring tone signal.The LT1684 uses its own ring tone output as a reference for generating local supply rails using complementary high voltage external MOSFETs as dynamic level-shifting devices. This 'active tracking' supply mode of operation allows linear generation of the high voltage ring tone signal, reducing the need for large high voltage filtering elements.