LT1684IS#PBF

Telecom Overview

The LT1684IS#PBF is a micropower ring tone generator manufactured by Analog Devices Inc. It accepts a user-generated pulse width modulated (PWM) input and converts it to a high voltage sine wave suitable for telephone ringing applications. The device features an active tracking supply configuration that allows linear generation of the ring tone signal, eliminating the need for high voltage post-filtering. Key electrical parameters include a DC supply current of less than 1mA, a differential input threshold of 0.5V to 1.0V, and an output short-circuit current capability of -190mA typical. The component operates within a temperature range of -40°C to +125°C and is housed in a 14-lead plastic SO package.

Telecom Feature Summary

• Capacitive isolation eliminates the need for optocouplers between the digital controller and the high-voltage ringer circuit.
• Active tracking supply configuration enables linear generation of the ring tone signal using external MOSFETs.
• Low distortion output meets international PTT requirements without requiring high voltage post-filtering.
• Differential input signal provides noise immunity against system transients.

Telecom Applications

• Wireless Local Loop Telephones
• Key System/PBX Equipment
• Fiber to the Curb Telecom Equipment

Telecom Procurement Notes

Verify the specific suffix #PBF indicates lead-free compliance status with the manufacturer before procurement. Confirm the industrial grade temperature rating (-40°C to +125°C) matches the target environment. Ensure the 14-pin SO package footprint aligns with the PCB design constraints. Check for any end-of-life notifications or discontinuance alerts from Analog Devices regarding this specific part number.

Telecom Selection Notes

Select the LT1684IS#PBF when designing telecommunication systems requiring isolated high-voltage ring tone generation. The industrial grade variant is necessary for environments operating below 0°C. Designers must provide external N-channel and P-channel MOSFETs for the active tracking supply rails. Ensure the PWM input signal maintains a minimum differential amplitude of 1.6V for valid switching.

Telecom Part Context

The LT1684 series serves as a specialized solution for generating telephone ringer signals directly from low-voltage digital controllers. The 'IS' designation identifies the industrial temperature grade version, while the 'S' indicates the 14-lead plastic small outline package. This component replaces traditional electromechanical ringer generators or complex discrete high-voltage driver circuits.

Telecom Replacement Considerations

LT1684CS: Commercial grade version with 0°C to 75°C operating range.

Telecom FAQ

How does the LT1684 handle high voltage isolation?

The LT1684 uses capacitor-isolated differential PWM input signals at pins IN A and IN B. This capacitive isolation eliminates the need for optocouplers while maintaining robustness against common mode glitches.

What is the function of the Active Tracking Supply?

The Active Tracking Supply uses the ring tone output as a reference to generate local supply rails via external MOSFETs. This allows the IC to linearly generate high voltage signals while maintaining approximately ±10V local supply rails across the chip itself.

Can the LT1684 operate without a PWM input?

Yes, by configuring the internal amplifier as a bandpass filter and using an external comparator like the LT1017 as a hard limiter, the LT1684 can form an active filter tuned oscillator to generate a sine wave without a PWM input.