Already available for sampling, the latest Class-D amplifier ICs from Analog Devices deliver an interesting set of features and specifications for highly efficient audio designs. The new MAX98415A and MAX98425A devices have been designed to support the development of new-generation portable and smart speakers, new streaming amplifiers, soundbars, and connected designs, as well as tablets, laptops, and desktop computers.
The MAX98425A is a high efficiency, ultra-low IQ, digital stereo Class-D IC, with best in class output efficiency thanks to its edge rate control and modulation scheme that enables filterless operation. This is an interesting medium power Class-D amplifier IC (27W 8Ohm stereo, with peak output current up to 6A) offering all possible means to conserve energy and achieve undistorted sound louder. It features digital PCM input (16kHz to 192kHz, I2S, left-justified, and TDM data formats) and internal digital volume control providing an attenuation range of 0dB to -90dB in 0.5dB steps. TDM modes support timing for up to 16 digital audio channels. It also offers noise gate, limiter and dynamic range compressor for low distortion reproduction. Limiter and dynamic range compressor settings can be tailored with particular driver to prevent gross driver overload.
To conserve energy with battery power, the MAX98415A IC uses variable power rail with dynamic-headroom tracking. The tracking mechanism can preserve consistent signal distortion and listening levels in the presence of a varying supply level. And the IC has a rich set of various protection algorithms: overcurrent, over-temperature, DC protection, brownout protection, offering a great choice for the different battery powered audio products and for soundbars.
Both devices support sample rates up to 192kHz and a higher passband (for fS > 50kHz) to enable high-resolution audio and ultrasound use cases. A separate bypass path is available for inputs, such as an ultrasound signal, so that it is not attenuated by audio processing. SSM and edge rate control minimize EMI and eliminate the need for output filtering found in traditional Class-D devices.
The Envelope Tracking algorithm on the devices monitors the incoming audio signal and generates a PWM signal to control an external DC-DC converter to keep the amplifier supply close to the peak output audio signal, thereby improving system efficiency, idle quiescent power consumption, and thermal efficiency.
For battery-powered applications, the BPE helps avoid a system brownout by reducing the device’s current consumption. This is achieved by either attenuating or limiting the amplifier output when the device supply drops below a set of programmable thresholds. In addition, as the amplifier supply varies due to sudden transients and declining battery life, DHT automatically optimizes the headroom available to the amplifier to maintain a consistent distortion level. Thermal foldback, when enabled, automatically reduces the output power when the temperature exceeds a user-specified threshold. This allows for uninterrupted music playback even at high ambient temperatures.
Both devices - MAX98425A and MAX98415A - are now available for sampling and production volumes. For developers, Analog Devices is already shipping the MAX98415/425AEVSYS evaluation boards.
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