July 03, 2020

National Semiconductor Introduces Two High-Performance, Low-Power Boomer Class D

National Semiconductor Corporation (NaTIonal Semiconductor CorporaTIon) announced the launch of two high-performance, low-power Boomer Class D audio subsystems to further expand the product lineup of this series of chips. The two new products are the LM49352 mixed-signal audio subsystem and the LM49151 analog subsystem, which are characterized by simplifying the system design of portable products, especially suitable for smart mobile phones, multi-function phones, portable electronic game consoles and portable global positioning System and other applications.

LM49352 is a mixed-signal audio subsystem with built-in audio codec, ground-referenced headphone amplifier, small earpiece driver, Class D speaker, and audio digital signal processor. These circuits are all built in 3.3mm x 3.3mm In a mini package. The efficiency of the built-in speaker is extremely high, and the efficiency can be as high as 93% when using 4.2V power supply to output 970mW. The headphone amplifier can support low power (18mW) MP3 playback function, which can further extend battery life.

The LM49151 analog subsystem has a built-in earphone driver, Class D speaker, ground-referenced headphone amplifier, and automatic level controller (ALC). These circuits are all built into a 2.2mm x 2.6mm ultra-small package. The power consumption of the LM49151 analog subsystem is lower than similar products. If it operates at 3.3V, the quiescent current of speakers and headphones can be as low as 7.3mA. Mobile phone manufacturers can make full use of the automatic level control function of this subsystem to flexibly control the distortion level of the audio signal to avoid speaker damage.

Main technical specifications and characteristics-LM49352 mixed signal audio subsystem

The full-featured LM49352 audio subsystem is packaged in a 36-ball micro SMDxt package. The built-in circuit includes a 24-bit stereo digital-to-analog converter, a 24-bit stereo analog-to-digital converter, a stereo headset amplifier, and a low Class D speakers with electromagnetic interference. In addition, this set of audio subsystem also has built-in two-line bidirectional I2S interface and PCM audio bridge circuit, which can easily connect peripheral devices such as Bluetooth module. Moreover, this system can also set different gains and modes through the I2C compatible interface.

If a 24-bit, 48kHz signal is input to the LM49352 subsystem, the signal-to-noise ratio of the built-in stereo analog / digital converter can reach 97dB; under the same circumstances, the signal-to-noise ratio of the digital / analog converter can reach 103dB. The speaker can use 4.2V power supply to provide up to 970mW output power to drive 8Ohm load, and the total harmonic distortion and noise is less than 1%.

The digital signal processor of the LM49352 subsystem has built-in special effect circuits that can support digital / analog converters and analog / digital converters, and can perform volume control, automatic level control (to compress and smooth signal spikes), and 5-band signal equalization ( In order to improve the audio processing effect) and other functions. In addition, the built-in analog / digital converter itself also has a flexible wind noise filter, so it can support voice or high-fidelity recording modes.

Main technical specifications and characteristics-LM49151 analog audio subsystem

The LM49151 audio subsystem is packaged in a 20-ball micro SMD package. The built-in circuitry includes a mono Class D speaker amplifier with enhanced emission suppression (E2S), a Class AB headphone driver, a ground-referenced stereo headset driver, Volume controller, input mixer / multiplexer and speaker protection circuit. This Class D amplifier uses a patented ultra-low electromagnetic interference pulse width modulation (PWM) architecture, which can greatly reduce the amount of RF signal radiation to ensure perfect sound quality.

The automatic level control (ALC) circuit of the LM49151 audio subsystem has many advantages. For example, the non-chopped automatic level control function can allow small signals to be amplified by multiples. Therefore, even if the battery voltage gradually drops, the signal will not be distorted, and the peak of the high-level signal will not be smoothed. In addition, the LM49151 chip can select the automatic level control function of the chopping level, which can not only output extremely high power, but also control the distortion level. In addition, the automatic level control function to select the power level can protect the speaker.

Price and availability

The unit price of the LM49352 chip is US $ 7.55, and the unit price of the LM49151 chip is US $ 1.60. Both chips use 1,000 chips as a purchase unit and have begun mass supply.

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