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LT1684

Micropower

Ring Tone Generator

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Allows Dynamic Control of Output Frequency,

Cadence, Amplitude and DC Offset

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Active Tracking Supply Configuration Allows Linear

Generation of Ring Tone Signal

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No High Voltage Post-Filtering Required

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Capacitive Isolation Eliminates Optocouplers

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Low Distortion Output Meets International

PTT Requirements

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Differential Input Signal for Noise Immunity

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User Adjustable Active Output Current Limit

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Powered Directly From High Voltage Ringer

Supply—No Additional Supplies Necessary

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Supply Current: < 1mA

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2% Signal Amplitude Reference

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Available in 14-Pin SO and DIP Packages

The LT

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 nor-

malizes 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.

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Wireless Local Loop Telephones

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Key System/PBX Equipment

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Fiber to the Curb Telecom Equipment

IN A

IN B

6.8nF

IRF9610

IRF610

100k

P1

µC

P2

OUT

COMP1

COMP2

AMPIN

100pF

1N4001

20pF

100pF

100pF

DC

ISOLATION

PWM

CONTROLLER

100

Ω

10k

10k

1N5817

0.1

µF

1

µF

3k

5k

2k

300k

6.8nF

100k

100

Ω

RING TONE

OUTPUT

±100mA

CAPABILITY

100V

+

–

–100V

LT1684

4700pF

1684 TA01

FB1

()

FB1: FERRONICS FMB1601

(716) 388-1020

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

, LTC and LT are registered trademarks of Linear Technology Corporation.

Electrically Isolated Ring Tone Generator