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Audio amplifiers for mobile phones and portable applications

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article image Contains a mono amplifier and stereo headphone amplifier.

NATIONAL Semiconductor, represented in Australia by Arrow Electronics , has released two Boomer audio amplifiers for mobile phones and portable applications. They deliver high sound quality and a high level of integration in a space-saving package.

The LM4845 audio subsystem integrates the audio amplifiers, volume control, mixer, eight output modes, power management control, 3D sound enhancement and I2C compatible control into a single package. The LM4888 stereo 2.1W speaker and headphone amplifier provide 3D programmability for the speaker and headphone, and ultra-low shutdown current for battery savings.

The LM4845 audio subsystem contains a mono amplifier and stereo headphone amplifier. The mono amplifier delivers 500mW of power into a mono 8Ω bridge-tied load with 1% total harmonic distortion plus noise (THD+N) from a 3.3V power supply. The stereo headphone amplifier delivers 25mW per channel of continuous average power into a stereo 32Ω load with 1% THD+N from a 3.3V power supply. The LM4845 stereo headphone amplifier can be configured for single-ended or output capacitor-less (OCL) operation.

It has a 32-step digital volume control and eight distinct output modes. The digital volume control, 3D enhancement and output modes are programmed through a two-wire I2C or three-wire SPI-compatible interface that allows flexibility in routing and mixing audio channels. This device has three input channels, one pair for a two-channel stereo signal and the third for a single-channel mono input. It delivers high-quality output power from a surface-mount package and requires only seven external components in the OCL mode and two additional components in the single-ended mode. The LM4845 also has a shutdown current of 0.1μA typical.

The LM4888 is a dual bridge-connected audio power amplifier which, when connected to a 5V supply, will deliver 2.1W to a 4Ω load or 2.4W to a 3Ω load with less than 1.0% THD+N. A user-selectable 3D enhancement mode provides enhanced stereo imaging. The LM4888 also has two separate headphone enable inputs, each having different logic level thresholds. Either headphone enable input activates the single-ended headphone mode and disables the bridge-tied load output mode. The headphone sense input is for use with a normal stereo headphone jack. The remaining input, headphone logic, accepts standard logic level thresholds. To simplify audio system design, the LM4888 combines dual bridge speaker amplifiers and stereo headphone amplifiers on one chip. Both the LM4845 and LM4888 feature low-power-consumption shutdown modes and thermal shutdown protection and also utilize circuitry to reduce “clicks and pops” during device turn-on.

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