Micropower Ring Tone Generator

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.

Applications

* Wireless Local Loop Telephones

* Key System/PBX Equipment

* Fiber to the Curb Telecom Equipment

* This product is pending obsolescence - Contact Analog Devices 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