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National Semiconductor launched a couple of low-power 'Boomer' Class D audio subsystems at the Globalpress Summit in San Francisco which are said to simplify the design of audio systems.
One of them, the LM49352, is a mixed-signal audio subsystem that integrates audio codec functionality with ground-referenced headphone amplifiers, earpiece driver, Class D loudspeaker and audio digital signal processor (DSP) in a 3.3 mm by 3.3 mm package. The loudspeaker delivers ultra-high efficiency (93 percent at 970 mW from a 4.2V supply), while the headphone amplifier offers low-power (18 mW) MP3 playback to extend battery life.
The other, LM49151, integrates an earpiece driver, Class D loudspeaker, ground-referenced headphone amplifiers and automatic level control (ALC) in an ultra-small 2.2 mm by 2.6 mm package. It consumes 7.3 mA of quiescent current at 3.3V for the loudspeaker and headphone. The subsystem's ALC feature provides handset manufacturers with a variety of options to control audio distortion levels and prevent speaker damage.
In a 36-bump micro SMDxt package, the LM49352 is a complete audio subsystem that includes stereo 24-bit digital-to-analog converters (DACs) and stereo 24-bit analog-to-digital converters (ADCs), stereo headphone amplifier and a low electromagnetic interference (EMI) Class D loudspeaker amplifier. The device features a dual bi-directional I2S interface and PCM audio bridge to enable easy interface to peripherals such as Bluetooth modules, as well as an I2C compatible interface for programming different gains and modes.
The LM49352's stereo ADC provides a signal-to-noise ratio (SNR) of 97 dB with a 24-bit, 48 kHz signal and the DAC provides an SNR of 103 dB with a 24-bit, 48 kHz signal. The loudspeaker amplifier delivers up to 970 mW to an 8-Ohm load with less than one percent harmonic distortion plus noise (THD+N) at 4.2V.
The LM49352's digital signal processing includes dedicated effects circuits for both the DACs and ADCs. These circuits include volume control, ALC with compression and limiting, and 5-band equalization (EQ) for quality audio processing. The ADC also is equipped with a flexible wind noise filter that can operate in voice or high fidelity recording mode.
In a 20-bump micro SMD package, the LM49151 audio subsystem includes a mono, enhanced emission suppression (E2S), Class D loudspeaker amplifier, Class AB earpiece driver, stereo ground-referenced headphone drivers, volume control, input mixer/multiplexer and speaker protection. The Class D amplifier features a patented, ultra-low EMI pulse-width modulation (PWM) architecture that reduces RF emissions while preserving audio quality.
The LM49151's ALC provides multiple benefits. Its no-clip ALC feature prevents distortion as battery voltages drop by allowing small signals to be amplified at high gains, while preventing clipping of high-level signals. In addition, the LM49151's clip-level select ALC produces high output power at a controlled distortion level, while the power-level select ALC provides speaker protection.
The LM49352 costs $7.55 and the LM49151 costs $1.60, both in 1,000-unit quantities.
David Manners, San Francisco
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