Texas Instruments LM4912MMBD

Overview

LM4912MMBD from National Semiconductor is a stereo headphone amplifier IC delivering 40mW per channel into 16Ω at 1% THD+N from a 3V supply, featuring ultra-low 10µV A-weighted output noise, 65dB PSRR at 1kHz, and integrated thermal shutdown - designed for portable audio systems including PDAs and CD players.

For engineers reviewing the LM4912MMBD datasheet, LM4912MMBD pinout, LM4912MMBD application, or LM4912MMBD equivalent, this page provides verified specifications, MSOP-10 package details, mute/shutdown timing behavior, gain configuration guidance, and real-world selection criteria for low-noise, low-voltage headphone amplification.

Technical Context

The LM4912MMBD integrates three operational amplifiers: two externally configurable gain channels (VoA, VoB) and one internal unity-gain buffer (VoC) providing half-supply bias. This architecture eliminates output coupling capacitors by maintaining DC bias at VDD/2 across both load terminals.

It operates from 2.0V to 5.5V, supports external gain-setting via Ri/Rf resistor ratio (AV = –Rf/Ri), and features independent logic-controlled shutdown (active-low SHUTDOWN pin) and mute (active-high MUTE pin), with <1mV output voltage change on release from shutdown and 10ms un-mute time.

Key Specifications

Pinout & Package

LM4912MMBD is housed in an MSOP-10 package (National Semiconductor package code MUB10A), measuring 3.0mm × 3.0mm × 0.85mm, optimized for space-constrained portable PCB layouts.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar stereo headphone amplifier applications.

Compared with LM4912MMBD, TPA6130A2RTJR delivers higher output power but forfeits capacitor-less operation and adds BOM complexity, while MAX4410ETE+ achieves lower noise but requires external circuitry for mute/shutdown - making LM4912MMBD optimal for balanced cost, size, and feature integration in mainstream portable audio.

Availability

LM4912MMBD is available at Aetrix Electronics and suitable for portable CD players, PDAs, and USB audio dongles requiring stable component supply, consistent parametric performance, and long-term lifecycle support.

Supply support for LM4912MMBD 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

National Semiconductor was a U.S.-based analog semiconductor company acquired by Texas Instruments in 2011, known for high-performance audio, power management, and interface ICs.

The LM4912MMBD belongs to the Boomer® family of headphone amplifiers, engineered specifically for low-noise, low-voltage, capacitor-less stereo audio delivery in space- and power-constrained portable electronics.

FAQ

What is the minimum supply voltage required for LM4912MMBD to deliver rated output power?

The LM4912MMBD operates from 2.0V to 5.5V. At 2.4V supply, it delivers 25mW per channel into 16Ω at 1% THD+N; full 40mW/ch requires ≥3.0V. Operation below 2.0V is outside specification and may cause instability or reduced PSRR. The LM4912MMBD maintains functional gain and noise performance across its full 2.0–5.5V range, but output power scales with V².

Does LM4912MMBD require output coupling capacitors?

No - the LM4912MMBD uses a patented capacitor-less architecture with an internal buffered mid-rail (VOC) output that biases both headphone terminals at VDD/2. This eliminates DC offset across the load, removing the need for large, costly output coupling capacitors typically required in single-ended headphone amplifiers. The LM4912MMBD thus reduces BOM count, PCB area, and low-frequency phase shift.

How does the shutdown function of LM4912MMBD differ from its mute function?

Shutdown (SHUTDOWN pin low) disables bias circuitry, reducing supply current to ≤2µA and powering down all amplifiers - wake-up takes ~2 seconds due to CB capacitor charging. Mute (MUTE pin high) holds outputs at VOC bias while disabling signal path, consuming ~3mA but enabling <10ms activation with <1mV transient. The LM4912MMBD supports both modes independently for flexible power/audio sequencing.

Can LM4912MMBD be used with 32Ω headphones, and what output power is achievable?

Yes - the LM4912MMBD is specified for 32Ω loads. At 3V supply, it delivers 25mW per channel at 1% THD+N into 32Ω; at 2.4V, output drops to 12mW/ch. Its low-output-impedance design ensures stable drive across impedance variations, and the 10µV noise floor remains effective even with higher-impedance transducers. For 32Ω use, the LM4912MMBD provides optimal balance of power, noise, and efficiency.

What is the purpose of the CB pin on LM4912MMBD, and what capacitor value is recommended?

The CB pin connects to a 4.7µF capacitor that stabilizes the internal VOC mid-rail buffer. This capacitor sets the time constant for shutdown entry/release and mute transitions - larger values increase pop suppression but slow response; smaller values improve speed but reduce PSRR. National Semiconductor specifies 4.7µF (tantalum or electrolytic) for optimal trade-off. The LM4912MMBD's CB network is essential for achieving its <1mV output voltage change on wake-up.