LM1875T/SL108949

Overview

The LM1875T/SL108949 is a monolithic Class-AB audio power amplifier manufactured by Texas Instruments. It delivers up to 30 watts of output power into 4Ω or 8Ω loads using ±25V to ±30V supplies. The device features extremely low distortion (0.015% at 1 kHz, 20W), a wide power bandwidth of 70 kHz, and an open-loop gain typically of 90 dB. Electrical characteristics include a supply voltage range of 16V to 60V, a maximum slew rate of 8 V/μs, and a gain-bandwidth product of 5.5 MHz. It incorporates internal current limiting, thermal shutdown with a parole circuit, and output protection diodes.

Feature Summary

• Advanced circuit techniques achieve very low distortion levels even at high output power.
• Internal overload protection includes current limit and sophisticated thermal shutdown with parole circuit.
• Wide supply range accommodates various single and dual power supply configurations.
• High current capability supports demanding load requirements.

Applications

• High performance audio systems
• Bridge amplifiers
• Stereo phonographs
• Servo amplifiers
• Instrument systems

Procurement Notes

Verify the specific ordering suffix SL108949 against the official TI Package Option Addendum. Standard production variants utilize suffixes such as NOPB or LFxx. Confirm that the requested part number corresponds to an active status and matches the required TO-220 package type before finalizing procurement specifications.

Selection Notes

Select this component for applications requiring high-quality audio amplification with minimal external components. Ensure the design maintains a closed-loop gain of 10 or greater for stability. Proper PCB layout is critical to prevent oscillation; separate ground paths for high-current outputs and low-level inputs are necessary to minimize distortion and noise coupling.

Part Context

This device belongs to the LM1875 family of audio power amplifiers from Texas Instruments. It is designed as a direct replacement for legacy National Semiconductor parts in consumer audio equipment. The series is characterized by its robust protection features and ability to deliver significant power in a plastic TO-220 package suitable for through-hole mounting.

Replacement Considerations

Standard replacements include LM1875T/NOPB and LM1875T/LF05. Verify pinout compatibility and thermal resistance requirements when substituting. Ensure the alternative part meets the same electrical specifications for supply voltage and output power capabilities.

FAQ

What is the minimum stable closed-loop gain for the LM1875?

The amplifier is internally compensated and stable for gains of 10 or greater.

How does the thermal protection circuit operate?

Shutdown occurs at 170°C die temperature and resumes at 145°C. If the fault persists, subsequent shutdowns occur at 150°C to reduce thermal cycling stress.