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Sophisticated Audio Amp Enhances Battery-Operated Mobile Products

Sept. 17, 2019
Sponsored by Digi-Key and Maxim Integrated: A new smart amplifier helps deliver the “Dynamic Speaker Management” system, which overcomes driving power issues related to micro speakers.

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Maxim Integrated’s new MAX98390 smart amplifier isn’t just another audio IC. It goes way beyond the expectations of most audio design engineers. This class D amplifier, which delivers high efficiency in battery-operated devices, adds many new features and capabilities not available elsewhere. If you’re designing portable equipment with an audio capability, the device may be a welcome alternative.

As consumer products continue to shrink, the desire to include audio hasn’t abated. Speakers have become smaller to accommodate this need, leading to a decline in audio quality. The most affected characteristics have been loudness and bass.

Increasing driving power is one way to overcome those deficiencies, but that can damage the speakers. Recognizing this problem, Maxim’s engineers went to work to solve this problem. The result is their Dynamic Speaker Management (DSM) system.

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Micro Speakers 101

The real problems lie in the micro speakers. Their diaphragms, coils, and magnets are significantly smaller, thereby limiting their ability to produce strong sound pressure and bass response. The diaphragm area is only in the 1- to 2.5-cm2 range and drive power is typically limited to 1 to 2 W to prevent speaker damage. Another critical limitation is the higher self-resonance of the speaker. Driving the speakers harder overcomes these deficiencies to a degree, but at the risk of thermal overheating and diaphragm over excursion.

The DSM solution is to use current and voltage monitoring and feedback plus a special audio algorithm to permit these small speakers to be driven beyond their limits without damage. The outcome is clean audio output with increased loudness and extended bass response with inherent protections.

The MAX98390

DSM is delivered by Maxim’s MAX98390 (see figure). This class D amplifier provides the high efficiency required of battery-operated devices. To help deliver the higher drive power, an integrated boost converter provides a supply voltage of up to 10 V to the amplifier with 2.65- to 5.5-V external dc input. Speaker output voltage and current are continually sensed and fed back to the DSM controller that implements the protection features. The serial digital audio is fed to the DSM circuits that provide the DSP algorithms to produce the stated features.

The MAX98390 is a class D audio amplifier with integrated boost converter, patented DSP processing algorithms, and full protection thanks to speaker voltage and current monitoring and feedback. Note the external inductor for the boost converter.

Some other features are output power in the 5.1- to 6.2-W range, depending on the external battery voltage and the limits on total harmonic distortion (THD). The system is able to accommodate 4- or 8-Ω speakers. Overall system efficiency can reach as high as 86% with a total quiescent power consumption as low as approximately 24 mW. PCM serial audio may come from I2S or 16-channel TDM sources. An I2C interface is provided for monitoring and control. The chip comes in a tiny 36-bump, 6.3-mm2 wafer-level package.


An essential complement to the MAX98390 DSM is the software that allows for customization for different end use cases.

The DSM Sound Studio software comes with the MAX98390EVSYS evaluation board, too. The whole package lets you implement a wide range of demos, and it provides super-fast speaker characterization, tuning, and evaluation. It eliminates the need to perform the complex and time-consuming processes used in the past to characterize different speakers.

A Success Story

PUI Audio, a large supplier of specialty audio products, recently used the MAX98390 in its ASE02506MS-LW90-DSM-R speaker. Thanks to Maxim’s DSM technology, this ultra-thin speaker delivers clean, clear, consistent sound for multiple applications. This chip plus the software tool box lets PUI provide custom speaker designs faster and easier.

For more on micro speakers, a video explains the similarities between a micro speaker and a standard speaker, and describes its three main components—the diaphragm, coil, and magnet. A micro speaker is torn down to show the various parts of the device, including its speaker driver.

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