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All-in-one audio subsystems target mobile phones and gaming

Fürstenfeldbruck, Germany – National Semiconductor has made two additions to its Boomer Class D audio subsystem family that are suited to smart phone, portable gaming device and portable GPS device designs.

The LM49352 mixed-signal audio subsystem integrates stereo 24bit digital-to-analog converters (DACs) and stereo 24bit analog-to-digital converters (ADCs), stereo headphone amplifier and a low EMI Class D loudspeaker amplifier, in a 3.3 x 3.3mm package. Among the features that NatSemi highlights is the efficiency of the loudspeaker (93 percent at 970mW from a 4.2V supply), while the headphone amplifier offers low-power (18 mW) MP3 playback to extend battery life. The stereo ADC integrated has a signal-to-noise ratio (SNR) of 97dB, whilst operating with a 24bit, 48kHz signal. The DAC, meanwhile, provides an SNR of 103dB using the same signal.

The LM49151 analog subsystem integrates an earpiece driver, Class D loudspeaker, ground-referenced headphone amplifiers in a 2.2 x 2.6mm package. Consuming 7.3mA of quiescent current at 3.3V for both loudspeaker and headphone, this has been designed as a low power alternative to discrete implementations. The loudspeaker features pulse-width modulation to reduce RF emissions while preserving audio quality. Another feature of the LM49151 is automatic level control (ALC), which allows handset manufacturers to control audio distortion levels and prevent speaker damage.

Both devices are already available, with samples and an evaluation board available from, National’s website .html.

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