Analog Devices Inc. LT1684IS#PBF

Overview

LT1684IS#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, <1mA supply current, ±1.25V amplitude-normalized BGOUT output, and user-adjustable current limiting. Used in wired telephone ringer circuits requiring international PTT-compliant low-distortion output.

For engineers reviewing the LT1684IS#PBF datasheet, LT1684IS#PBF pinout, LT1684IS#PBF application, or LT1684IS#PBF equivalent, key selection criteria include its differential PWM receiver with 1.6V minimum threshold, active tracking supply enabling linear ±100V output swing, 14-pin SO package, 0°C to 125°C industrial temperature range, and compliance with international telephone ringing standards.

Technical Context

The LT1684IS#PBF implements a differential PWM receiver with ±100mV hysteresis beyond thresholds, normalizing input to ±1.25V referenced to OUT. Its active tracking supply uses GATE+ and GATE– pins to bias external N- and P-channel MOSFETs, generating local ±10V rails self-referenced to the high-voltage output signal.

The IC integrates a two-pole active filter/amplifier driven by BGOUT, with COMP1 and COMP2 pins supporting external compensation. Output current limiting is implemented via LIM+ and LIM– pins using V_BE-based clamping, with typical ±190mA short-circuit capability when pins are directly tied.

Key Specifications

Pinout & Package

LT1684IS#PBF is housed in a 14-lead plastic SOIC (S package), 7.5 mm × 8.75 mm body, 1.27 mm pitch, JEDEC MS-012AC compliant. Pin 1 is IN B, pin 14 is IN A; top-view numbering follows standard SOIC convention.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT1684CS#PBF, the LT1684IS#PBF offers superior thermal performance in reflow-soldered industrial systems; compared with MAX14951AETA+, it delivers certified low-distortion ringing via analog-active architecture but requires external MOSFETs and careful filter design.

Availability

LT1684IS#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 temperature ranges and long production lifecycles.

Supply support for LT1684IS#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors for precision signal conditioning and power conversion.

The LT1684 product line was designed specifically for telecom ring tone generation in isolated, high-voltage analog interfaces-emphasizing micropower operation, differential noise immunity, and PTT-compliant waveform fidelity without transformers or optocouplers.

FAQ

What is the operating temperature range for the LT1684IS#PBF?

The LT1684IS#PBF is specified for an industrial-grade operating junction temperature range of –40°C to +125°C. This rating is confirmed in the Absolute Maximum Ratings table and applies to the IS-grade variant. Thermal performance is characterized with θ_JA = 115°C/W in the 14-lead SO package, making it suitable for deployment in uncontrolled telecom cabinets and outdoor network terminals.

Does the LT1684IS#PBF require external MOSFETs to function?

Yes, the LT1684IS#PBF requires external N-channel and P-channel high-voltage MOSFETs (e.g., IRF610 and IRF9610) connected to GATE+ and GATE– pins to implement its active tracking supply architecture. These FETs generate the local ±10V supply rails referenced to the high-voltage output. Without them, the IC cannot bias its internal circuitry for linear ring tone generation.

How does the LT1684IS#PBF achieve PTT-compliant low distortion?

The LT1684IS#PBF achieves PTT-compliant low distortion through its active tracking supply architecture, which maintains linear amplifier operation across the full ±100V output swing. Unlike switched-capacitor or transformer-based approaches, this method avoids saturation and crossover distortion. The datasheet explicitly states "Low Distortion Output Meets International PTT Requirements" as a core feature.

Can the LT1684IS#PBF generate ring tones without a PWM input signal?

Yes-the LT1684IS#PBF can be configured as an active filter tuned oscillator by connecting its amplifier and BGOUT buffer in a positive feedback loop with external resistors and capacitors. Application Note 1684 F05a shows a complete implementation eliminating the need for external PWM generation, producing stable 20 Hz or 25 Hz sine waves directly from DC power.

What is the purpose of the ATREF pin on the LT1684IS#PBF?

The ATREF pin on the LT1684IS#PBF serves as the reference node for the active tracking supply system. It is typically shorted to OUT and functions as the floating "ground" for internal biasing. The GATE+ and GATE– outputs self-bias relative to ATREF, enabling the IC to maintain stable ±10V local supplies while the output swings hundreds of volts-this is fundamental to its linear high-voltage operation.