The miniaturization of consumer devices requires speakers to fit within smaller form factors, which has led to more applications moving towards the use of microspeakers. As speakers shrink, loudness or sound pressure level (SPL) decreases while the resonant frequency increases, leading to less bass. Driving the speakers harder to increase loudness and bass response can easily damage the microspeakers through overheating and over excursion.
The new MAX98390 Smart Amplifier solves this challenge by utilizing integrated IV (current and voltage) sense and Maxim's DSM algorithm to drive speakers to their maximum specified limits, while protecting against over excursion and over-temperature events. DSM's thermal protection empowers designers to safely push their speakers well beyond their specified power rating enabling the speakers to produce their maximum loudness. DSM's excursion protection enables designers to drive speakers to their specified excursion limits, producing sound up to two octaves below the resonant frequency limit. Effectively, the MAX98390 delivers up to 2.5x loudness (Sound Pressure Level) and up to 2 octaves deeper bass versus conventional 5V amplifiers in a small form factor.
To properly protect the speaker, amplifier algorithms must know the characteristics of the speaker, such as resonant frequency within its enclosure, excursion limit and voice coil thermal limit. Traditionally, designers had to go through the time-consuming and complex characterization process or rely on direct supplier support to characterize their speakers and enclosures. This challenge is further exacerbated as most projects start prototyping with multiple speakers per project, requiring several weeks of supplier support or requiring special equipment and expertise.
The MAX98390 significantly reduces the design time through the easy-to-use DSM Sound Studio GUI that allows users to quickly and easily characterize many speakers. Combined with DSM's thermal protection, the result is maximum loudness across the significantly extended frequency ranges in minutes, with no complex programming required. To cater to the miniaturization of devices and shrinking batteries, the MAX98390 offers industry-leading peak efficiency at 86 percent, which is even further improved with DSM's Perceptual Power Reduction (PPR) feature that can yield up to an additional 25 percent efficiency, and the lowest quiescent power consumption of ~24mW, making it the ideal choice for low power devices that need longer battery life.
The MAX98390 is a high-efficiency mono Class-D DSM smart amplifier that features an integrated boost converter, integrated Dynamic Speaker Management, and FET scaling for higher-efficiency at low output power. The maximum boost converter output voltage is programmable from 6.5V to 10V in 0.125V increments from a battery voltage as low as 2.65V. The boost converter supports bypass mode for lower quiescent current and improved mid-power efficiency as well as envelope tracking which automatically adjusts the output voltage for maximum efficiency. The boosted supply efficiently delivers up to 6.2W at 10% THD+N into a 4Ω load.
The PCM interface supports I2S, left-justified, and 16-channel TDM formats as a slave or master device with I2C control. Either BCLK or MCLK can be used as the internal clock source providing system level flexibility. Patented active emissions limiting edge rate and overshoot control circuitry minimizes EMI and eliminates the need for output filtering found in traditional Class-D devices. A flexible brownout-detection engine (BDE) can be programmed to initiate various current limiting, signal limiting, and clip functions to prevent dips in battery voltage. Threshold, hysteresis, and attack-and-release rates are programmable.
The IC is available in a 0.4mm pitch, 36-bump wafer-level package. It is specified over the extended -40°C to +85°C temperature range. On-chip DC resistance (Rdc) testing can be used on the production line for quality assurance to ensure speaker is within impedance tolerance.
"Meeting customers' audio expectations given available size and power constraints gets tougher each day," says Michael Van Den Broek, senior applications engineer for PUI Audio. "Having a simplified turnkey solution like the MAX98390 in our toolbox to increase the ability of our micro speakers makes the job easier and our customers much happier—which is the ultimate goal."
"The MAX98390 smart amplifier was designed to boost audio quality in the smallest form-factor to make it nimble enough to go into any device," adds Greg Mow, business manager for Mobile Audio Solutions at Maxim Integrated. "From providing the most balanced and loudest sound to offering the market's highest efficiency and ease of design, the MAX98390 enables our customers to deliver a best-in-class, immersive sound experience."
The MAX98390EVSYS# evaluation kit is available for $200.