Analog Devices Inc. LT1684CS#PBF

Overview

LT1684CS#PBF from Analog Devices (formerly Linear Technology) is a micropower telecommunication ring tone generator IC that converts capacitor-isolated differential PWM input into high-voltage sine-wave ringing signals. It features active tracking supply architecture, ±1.25V amplitude-normalized BGOUT output, <1mA supply current, and supports 17Hz–50Hz ring frequencies for telephone line interface applications.

For engineers reviewing the LT1684CS#PBF datasheet, LT1684CS#PBF pinout, LT1684CS#PBF application, or LT1684CS#PBF equivalent, this page delivers verified functional identity, confirmed 14-pin SO package mapping, validated pin roles (e.g., GATE+, LIM+, ATREF), real-world ripple rejection performance (≥40dB at 10kHz), and two field-validated alternative parts with documented electrical and application differences.

Technical Context

The LT1684CS#PBF implements a differential PWM receiver with 1.6V minimum valid input threshold and ±100mV hysteresis, normalizing signal amplitude to ±1.25V referenced to OUT. Its active tracking supply uses external high-voltage MOSFETs (e.g., IRF610/IRF9610) to generate local ±10V rails dynamically referenced to the ring output voltage-enabling linear amplification of ±100V peak signals without post-filtering.

The output stage integrates a dual-compensated (COMP1/COMP2) amplifier with user-adjustable current limiting via LIM+ and LIM– pins, supporting ±100mA peak drive into telecom loads up to 7 REN. The BGOUT buffer provides 1.25V bandgap-referenced PWM output with 160–300ns rise time and ±4.5mA short-circuit protection.

Key Specifications

Pinout & Package

LT1684CS#PBF is housed in a 14-lead plastic SO (SO-14) package with standard JEDEC MS-012AC dimensions (8.65mm × 3.90mm × 1.75mm), gull-wing leads, and 1.27mm pitch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar ring tone generator applications.

Compared with LT1684CS#PBF, LT3580EMS#PBF eliminates external MOSFETs but sacrifices isolation and programmability, while MAX14951ATJ+T offers faster time-to-market at the cost of flexible ring profile generation-LT1684CS#PBF remains optimal for designs requiring field-upgradable tone parameters and telecom-grade surge immunity.

Availability

LT1684CS#PBF is available at Aetrix Electronics and suitable for wireless local loop telephones, key system/PBX equipment, and fiber-to-the-curb telecom equipment requiring stable component supply across extended product lifecycles.

Supply support for LT1684CS#PBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices acquired Linear Technology in 2017 and maintains full technical and manufacturing continuity for the LT® product family, including precision analog and power management ICs for demanding industrial and telecom applications.

The LT1684CS#PBF belongs to Linear Technology's telecommunication interface product line, designed specifically for high-reliability, isolated ring tone generation in next-generation voice infrastructure equipment.

FAQ

What is the primary function of the LT1684CS#PBF in a telephone line interface?

The LT1684CS#PBF serves as a micropower ring tone generator that converts differential PWM input into high-voltage sine-wave ringing signals compliant with international PTT standards. It uses active tracking supply architecture to generate ±100V peak outputs directly from the telephone line voltage, eliminating need for post-filtering or optocouplers-making LT1684CS#PBF ideal for isolated telecom ringer circuits.

How does the active tracking supply feature of the LT1684CS#PBF improve system efficiency?

The active tracking supply in LT1684CS#PBF uses the ring output itself as a reference to dynamically generate local ±10V supply rails via external MOSFETs (e.g., IRF610/IRF9610). This allows linear amplification of ±100V signals while maintaining low internal voltage stress-reducing heat dissipation, eliminating large high-voltage filter capacitors, and cutting total solution size by up to 40% compared to conventional approaches. LT1684CS#PBF achieves this with only <1mA quiescent current.

Can the LT1684CS#PBF operate without a PWM input signal?

Yes-the LT1684CS#PBF supports active filter tuned oscillator mode, enabling standalone sine-wave generation without external PWM. By configuring its amplifier as a high-Q bandpass filter and combining it with a hard limiter (e.g., LT1017 comparator), LT1684CS#PBF produces stable 20Hz or 25Hz outputs. Component values (RF1–RF3, CF1–CF2) set frequency and amplitude-allowing LT1684CS#PBF to replace both PWM controller and tone generator in cost-sensitive VoIP gateways.

What are the absolute maximum voltage ratings for the GATE+ and GATE– pins of the LT1684CS#PBF?

The GATE+ and GATE– pins of LT1684CS#PBF have an absolute maximum differential rating of –0.3V to 42V (GATE+ – GATE–). Their individual voltage ranges are constrained relative to V+ and V–: GATE+ must stay within (V+ – 7.0V) to (V+ + 0.3V), and GATE– within (V– – 0.3V) to (V– + 7.0V). These limits ensure safe biasing of external N- and P-channel MOSFETs like IRF610 and IRF9610 in active tracking configurations-critical for robust LT1684CS#PBF operation in high-voltage telecom environments.

How does the LT1684CS#PBF achieve compliance with international PTT ringing requirements?

The LT1684CS#PBF meets international PTT requirements through low-distortion output (<25mVP-P ripple on ±100V sine waves), differential input noise immunity (1.6V threshold with ±100mV hysteresis), and built-in current limiting (±100mA peak). Its 2-pole MFB active filter achieves >40dB carrier rejection at 10kHz, satisfying ITU-T K.20 surge immunity and spectral purity mandates-verified in typical applications like wireless local loop telephones and fiber-to-the-curb equipment using LT1684CS#PBF.