LT1684CS#TRPBF

Telecom Overview

The LT1684CS#TRPBF is a micropower ring tone generator designed for telecommunication applications. It converts user-generated pulse width modulated (PWM) input signals into high voltage sine waves suitable for telephone ringing. 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 and a normalized PWM buffered output magnitude of 1.25V. The output amplifier provides a typical short-circuit current limit of -190mA to 350mA depending on configuration. 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 by accepting differential PWM inputs.
• Active tracking supply configuration enables linear generation of high voltage ring tone signals without large filtering elements.
• Low distortion output meets international PTT requirements with dynamic control over frequency, cadence, amplitude, and DC offset.
• User-adjustable active output current limit protects the device during operation.

Telecom Applications

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

Telecom Procurement Notes

Verify the specific suffix #TRPBF indicates tape and reel packaging when sourcing components. Confirm the industrial grade designation (IS) aligns with the required operating temperature range of -40°C to +125°C. Ensure compatibility with the 14-lead SO package footprint during PCB layout. Check for any end-of-life notifications or discontinuance notices from Analog Devices prior to final design approval.

Telecom Selection Notes

Select this component for designs requiring isolated ring tone generation with minimal external filtering. The active tracking supply feature simplifies high-voltage circuit design by maintaining local supply rails relative to the output signal. Ensure the external MOSFETs selected for the active tracking stage have sufficient VDS ratings to handle the peak output voltage plus supply rail excursions. Verify that the PWM controller can provide the required minimum differential input voltage of 1.6V.

Telecom Part Context

The LT1684 series includes variants such as LT1684CN, LT1684CS, LT1684IN, and LT1684IS. The CS suffix denotes the commercial temperature range variant in a 14-lead SO package, while IS indicates the industrial temperature range. The TRPBF suffix specifies the tape and reel packaging format with lead-free plating. All variants share the same functional block diagram and pinout configuration.

Telecom Replacement Considerations

Public confirmed substitute part numbers are not available in the provided documentation. Designers should evaluate the LT1684IS#PBF for industrial temperature requirements or LT1684CS#PBF for tube packaging if the TRPBF version is unavailable. Cross-referencing with other telecom ringer ICs may be necessary if the LT1684 series is discontinued.

Telecom FAQ

How does the LT1684 generate the ring tone signal?

The LT1684 accepts a capacitor-isolated differential PWM input encoded with ring tone information. An internal active filter/amplifier extracts the low-frequency component to produce a high voltage sine wave output.

What is the purpose of the active tracking supply?

The active tracking supply uses external MOSFETs to generate local supply rails that track the output signal voltage. This allows the IC to linearly generate high voltage outputs while maintaining stable internal supply voltages, reducing the need for large high voltage filtering components.

Can the LT1684 operate without a PWM input?

Yes, the LT1684 can be configured as an active filter tuned oscillator. By connecting a high-Q bandpass filter and a hard limiter in a positive feedback loop, it can generate a sine wave without an external PWM signal.