Analog Devices Inc. LT1684IN#PBF

Overview

LT1684IN#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 up to ±100V peak, with active tracking supply architecture, <1mA quiescent current, and ±100mA output drive capability for telephone line interface applications.

For engineers reviewing the LT1684IN#PBF datasheet, LT1684IN#PBF pinout, LT1684IN#PBF application, or LT1684IN#PBF equivalent, key selection considerations include its differential PWM receiver with 1.6V minimum threshold, ±1.25V normalized BGOUT output, active tracking supply operation enabling linear high-voltage generation without post-filtering, and support for international PTT-compliant low-distortion ring tones in wireless local loop and PBX systems.

Technical Context

The LT1684IN#PBF implements a differential PWM receiver with 7kΩ–10kΩ overdrive impedance and ±100mV hysteresis beyond thresholds, normalizing input to ±1.25V referenced to OUT. Its active filter/amplifier stage uses COMP1 and COMP2 pins for dual-pole compensation and supports configurable MFB topologies.

Local supply rails (V+ and V–) are dynamically generated via external N- and P-channel MOSFETs biased by GATE+ and GATE–, self-referenced to ATREF and tracked to the ring output-enabling ±10V internal rail operation while delivering ±100V output swing. Current limiting at LIM+ and LIM– provides ±100mA min/±190mA typ sink/source capability with external resistor programmability.

Key Specifications

Pinout & Package

LT1684IN#PBF is housed in a 14-lead plastic DIP (N package) with 0.3-inch body width and standard through-hole footprint. Pin 1 is IN B, pin 14 is IN A, and pin 8 is the high-current OUT terminal. All pins are electrically isolated from digital control side via capacitor coupling.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT1684IN#PBF, LT1684IS#PBF offers identical functionality in a smaller SOIC package but reduced thermal performance, while MAX14951AETA+ replaces the active tracking architecture with an integrated H-bridge-reducing component count at the cost of higher quiescent power and loss of analog PWM flexibility.

Availability

LT1684IN#PBF is available at Aetrix Electronics and suitable for wireless local loop telephones, key system/PBX equipment, and fiber-to-the-curb telecom hardware requiring stable component supply, long-term industrial temperature support, and PTT-compliant ring tone generation.

Supply support for LT1684IN#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. (including former Linear Technology products) designs precision analog, mixed-signal, and power management ICs for high-reliability industrial, automotive, and communications applications.

The LT1684IN#PBF belongs to Linear Technology's telephony interface product line, engineered specifically for high-voltage, low-power, electrically isolated ring tone generation in legacy and next-generation telecom infrastructure.

FAQ

What is the absolute maximum voltage rating for the LT1684IN#PBF GATE+ and GATE– pins?

The LT1684IN#PBF GATE+ and GATE– pins have an absolute maximum differential voltage rating of –0.3V to 42V. This allows safe operation with external MOSFETs handling up to ±120V rail swings when used in active tracking configurations. Exceeding this range risks permanent damage to the internal gate drive circuitry, so proper FET selection and gate resistor sizing per the datasheet is essential for reliable LT1684IN#PBF deployment.

Can the LT1684IN#PBF generate ring tones without a PWM input signal?

Yes-the LT1684IN#PBF can be configured as an active filter tuned oscillator by connecting its amplifier stage in positive feedback with a hard limiter (e.g., LT1017 comparator), eliminating the need for external PWM. This topology generates a clean 20Hz or 25Hz sine wave autonomously. The LT1684IN#PBF's COMP1/COMP2 pins and AMPIN input support this mode, and application note 1684 F05a provides a validated schematic using IRF610/IRF9610 FETs and 0.22µF capacitors.

What is the purpose of the ATREF pin on the LT1684IN#PBF, and how must it be connected?

The ATREF pin on the LT1684IN#PBF serves as the reference node for the active tracking supply circuitry, where GATE+ and GATE– bias currents sum. In standard operation, ATREF must be shorted to OUT to establish the floating local supply rails (V+ and V–) referenced to the ring output. Leaving ATREF unconnected or misrouting it breaks the tracking loop, causing supply collapse and output failure-so correct ATREF-to-OUT connection is mandatory for functional LT1684IN#PBF operation.

How does the LT1684IN#PBF achieve low distortion while meeting international PTT requirements?

The LT1684IN#PBF achieves low distortion through three integrated design elements: (1) differential PWM input with hysteresis and common-mode rejection, (2) bandgap-referenced ±1.25V BGOUT normalization ensuring amplitude stability, and (3) linear active filter architecture with COMP1/COMP2 compensation minimizing phase nonlinearity. These features collectively maintain THD below PTT-specified limits across –40°C to +125°C, making the LT1684IN#PBF compliant for global telecom certification without external trimming.

What external components are mandatory for basic LT1684IN#PBF operation?

Four external components are mandatory for basic LT1684IN#PBF operation: (1) 100pF AC-coupling capacitors on IN A and IN B pins, (2) 10kΩ series resistors for transient protection on both PWM inputs, (3) 100pF capacitor from COMP1 to OUT, and (4) 20pF capacitor from COMP2 to OUT. Additionally, external N- and P-channel MOSFETs (e.g., IRF610/IRF9610) and gate pull-up/down resistors are required for active tracking supply generation-omitting any of these prevents functional LT1684IN#PBF output.