Stereo Headphone Amplifiers Developed For Portable Apps

By employing an output capacitor-less (OCL) design, the LM4910 stereo headphone amplifier eliminates the two output coupling capacitors normally needed in headphone applications, while the LM4911 amp offers a selectable OCL mode or capacitive coupled mode. Part of the Boomer portfolio of audio ICs, the 5V amplifiers are ideally suited for use in stereo headphones for mobile phones, PDAs, MP3 players, and other portable electronic products. The LM4910 audio power amp can deliver 35 mW of continuous average power to a 32-ohm BTL load with less than 1% distortion from a 3.3V supply. And it contains advanced pop-and-click circuitry that eliminates noises caused by transients that normally occur during turn-on and turn-off. Other LM4910 features include a low power consumption shutdown mode, activated by driving the shutdown pin with logic low, and a thermal shutdown protection mechanism. It also is unity-gain stable. The LM4911 amp can deliver 40 mW per channel of continuous average power into a 16-ohm load, or 25 mW into a 32-ohm load at 1% THD from a 3V supply. It also features a low-power consumption shutdown mode and a power mute mode that allows for faster turn-ons with less than 1 mV voltage change at outputs on release. The power amp also has an internal thermal shutdown protection mechanism and is unity-gain stable. The LM4910 comes in 8-pin SOIC and MSOP packages and the LM4911 is housed in 8-pin MSOPs, with both devices priced at $0.75 each/1,000. NATIONAL SEMICONDUCTOR CORP., Design Support Group, Santa Clara, CA. (800) 272-9959.